The needle is still going strong as it swings for the last marking on the dial, 160mph, when the acceleration abruptly but smoothly tails off - we've hit the 155mph speed limiter, and there's still a chunk of the straight to go. Jethro utters a raw expletive.
How fast would the E55 go if there was no limiter and the straight was two miles long? One eighty? Easily. 200? Possibly. A derestricted SL55 with essentially the same 5.4-litre supercharged V8 made monkeys of a bunch of supercars at a Nardo test organised by Auto Motor und Sport magazine, topping out at 202mph and proving the most accelerative up to 170.
A couple of months ago we attached our own VBOX timing gear to an SL55: 0-60 in 4.6sec and 0-150 in 24.0. Quick, huh? Yeah, but the more sober-looking E55 gets to 150mph in just 22.8sec... [insert your own expletive here].
In at least one respect, the E55 redefines the term 'performance saloon'. In this class there isn't a quicker or more powerful four-door; with 469bhp the Merc has 25bhp in hand over its most potent rival, the Audi RS6, and almost 70bhp over the iconic BMW M5. In the time the Mercedes takes to get to 150mph, the Audi and BMW have just passed 130mph. And in terms of torque the E55 is even more impressive, its supercharged V8 generating an incredible 516lb ft, over 100lb ft more than the twin-turbo RS6 and no less than 147lb ft (almost 40 per cent) more than the normally aspirated M5.
If this was a game of Top Trumps, you'd feel pretty confident with the E55 AMG in your hand. However, whether you'd feel so invincible with its steering wheel in your palms and a challenging road unfurling before you is more what evo is about. Having the power is one thing, making it effective, exploitable and enjoyable is quite another. 'Power is nothing without control', as Pirelli says.
Power has its price, too; at £60,640 the E55 costs over £8000 more than the M5 and about £3000 more than the RS6, though here the gap to the Audi is less because we've chosen the five-door Avant which has distinctly more supple suspension than the saloon.
However, view the E55 as a four-door, stealth-specification SL55 and it doesn't look so expensive. And stealthy it certainly is - it could be any version of the new E-class with optional AMG five-spoke alloys, only the quartet of tailpipes and a few discreet badges revealing its true identity. Another car that makes it look like a bargain is the Brabus EV12 that we drove back in issue five. The E55 is actually more accelerative than the 574bhp, 206mph Brabus (verified by the Guinness Book of Records as the fastest saloon car in the world), and it costs about half the price.
It was a perfect day when we turned up at Millbrook to figure the Merc - very cold, providing the dense air that the supercharger loves, and perfectly dry. On the ultra smooth asphalt, the auto-only E55 hooked up reasonably well and with no effort other than a stretching of the right leg bagged 0-60 in under five seconds and 0-100 in the low 10s. Incredible. We shaved off a mere tenth by switching ESP off and resorting to road tester skill, which shows how carefully optimised the system is, and how much the E55 relies on it - many runs were slower because the rear tyres lit up and squandered the performance.
Compared with the SL55, the AMG E-class has a slightly lower power rating but that isn't the reason it can't quite match the SL's take-off. It has narrower rear tyres, is almost 200kg lighter (weight helps traction), and also has a longer wheelbase, so there's a smaller degree of helpful weight transfer to the rear on take-off. So with less launch bite, the E55 is a couple of tenths behind the SL up to 60mph (4.8 versus 4.6sec), but once traction has ceased to be an issue it closes the SL down. By 100mph it has drawn level on 10.2sec and by 150mph it's over a second ahead.
Genuine supercars don't go much faster, so it's no surprise that the Audi and BMW are left in the Mercedes' wake. They're pretty evenly matched, but with its six-speed manual and rear-drive, there's a lot more technique involved in getting the M5 off the line to hit 60mph in 4.9sec and 100 in 11.5. With no special driver skill the automatic, four-wheel-drive RS6 will knock off 60 and 100mph in around 5 and 12 seconds all day but by turning off wheelspin control, holding it against the brakes and dialling in 3000rpm, it's possible to launch harder and get them down to 4.8 and 11.6.
If you're tempted to think that on real roads the E55 won't feel that much quicker than its rivals, you'd be wrong. If anything, it feels more terrifyingly rapid than it did at the test track. The amount of thrust it can summon up seemingly in an instant is at times genuinely shocking. Don't be tempted to ferry fragile relatives around when you've got hay fever. The supercharged V8's peak torque - that truly monumental 516lb ft - arrives at just over 2500rpm, and the elastic nature of the auto 'box's fluid flywheel means that the engine hits those revs only a moment or two after the accelerator finds the carpet.
The RS6 feels mighty quick when you stoke its rumbling, twin-turbo V8 up to full boost, no question. It delivers the sort of thrust that warrants a warning on its cup holders advising that full-power kickdown whilst carrying hot beverages is not recommended. And yet there's no doubt the E55 hits even harder and faster, exposing a minimal amount of lag that you otherwise wouldn't notice. Similarly, its linear, unrelenting thrust points up a slight flattening of the Audi's delivery in the mid-range.
After this pair you have to consciously adapt to the BMW. It's so easy to forget it's a manual and sit there wondering why it's labouring in sixth when you've floored the throttle to overtake. Doh! The long, knuckly shift of the M5 has never been its best feature but after a while it becomes less obvious and it does give instant, direct access to the engine's performance.
Hooked up to the appropriate ratio, the normally aspirated 5-litre V8 doesn't feel massively out-gunned by the forced induction V8s ranged against it, responding instantly and pulling for the redline with ever increasing and wholesome honesty - organic is the word that springs to mind.
The M5 never delivers the knock-out thump of the E55, and what makes the Mercedes' sledgehammer thump all the more stunning is the fact that when you're just bimbling it feels like a regular, comfortable executive saloon. It rides over shoddy asphalt with suppleness, the gearbox shuffles the ratios almost seamlessly and the V8 is much less vocal than it is in the SL55. There are pointers that it's not your average E-class: deeply bolstered, snug-fitting seats, a leather-clad wheel that's small by Mercedes standards and a lovely set of AMG logo'd charcoal grey on opaque white dials.
There's a meaty weighting to the E55's steering but it's not as responsive as you'd expect. It feels right a few degrees either side of centre but the first time you heft the Merc into a quick, moderately tight bend, the nose doesn't turn as much as anticipated. It's almost as if the steering ratio changes, becomes slower, as you approach a quarter of a turn of lock. You gradually adapt to it, but after a stint in the M5 or RS6, the first decent turn reminds you it's not quite right.
If the E55's rear tyres had to survive without ESP, they would lead a short and violent life. Only two tyres are approved for it, a Dunlop and the Continental Sport Contact 2s fitted to this car, whose sidewalls carry the words 'Extra Load'. I imagine they have additional banding in the carcass to prevent the branding on the sidewalls becoming permanently distorted by the shearing loads between the rim and the tread chewing at the tarmac. Well, in perfect conditions, at least.
If the road surface is cold, bumpy or at all greasy, the 265/35 ZR18s simply can't find enough purchase below 60mph to use all of the engine's massive grunt. Try to use much more than half throttle and the ESP traction control goes into overtime, its warning light flickering like it's sending a semaphore message. To its credit, ESP does a marvellous job and lives up to its monicker, shutting down wheelspin before it gets a chance to jab the tail out of line more than a few degrees and then feeding the power back in keenly but cautiously and remarkably smoothly.
There are lots of nudges and squirms at the rear axle which you discover aren't solely down to ESP intervention (when you get either brave or foolish enough to turn the system off). And if the speed is high enough to give the tyres the chance to hold the road, you can feel a gentle shimmy as the level of grip on each side changes.
Still, you'd reckon that with so much power on tap, the E55 would be a doddle to power-slide, right? Er, no. Although it lacks a limited slip diff, there's enough torque to get both wheels spinning and arc you into a slide (so far, so good) but the steering weighting changes after you've got the lock on and stabilised things, loading up when you try to wind a bit of lock off to trim your line. Alternatively, on a wet road the power escapes through one fizzing rear tyre, then the other, and then - just when you've given up hope of it sliding - both of them. Whoa! That's very exciting, I assure you.
You look to the M5 with its long-established reputation to show how a big performance saloon should behave, and once you've slipped behind the wheel, it feels more right - the driving position is lower and you feel more sucked-in, more a part of the car. Its ride feels initially tauter but it's a surprise to see its traction control light flashing almost as often as the Merc's was on the same greasy roads.
The BMW's normally aspirated 5-litre V8 doesn't have anything like the low-end surge of the force-fed Merc and Audi V8s but work it through the rev range and it gains lusty strength and purpose above 4000rpm, lunging for the redline with a hard yet refined eight-cylinder whirr. The sensation of a big, heavy car beneath you is ever present but the difference is that after a few miles your tentative extending of the throttle and pushing against the grip in corners is building rather than eroding your confidence.
For the keen driver there are two advantages that the M5 has over the E55 that can't be underestimated - the first is that it's normally aspirated, the second that it's manual. Together, they allow so much more control and precision when you're feeling your way but trying to go quickly. If you're up for it and you disengage DSC (Dynamic Stability Control), when the M5's tail slips mid-bend you can hold a steady throttle and ride it out, or even add a bit more throttle at the exit for a flourish of opposite lock. Its steering is light enough for easy handling around town yet weighted just-so for confident A- and B-road work, and there's decent feel through its fat rim, too.
No question, you have to be confident to play an M5 beyond its grip because it's a hefty car but, compared with the E55, whenever you push harder, the picture coming through the wheel and seat sharpens rather than softens. Simply put, at the end of a rapid drive in the Merc, you feel you've survived. In the BMW, you want to go for a few more miles.
And then there's the RS6. Initially, it's not so much the performance of its twin-turbo V8 that impresses but the fact that it has the traction - thanks to four-wheel drive, of course - to use every last ounce of the 444bhp that it delivers, almost all the time. Its traction control light might flicker occasionally but you rarely feel any electronic throttling back.
In fact, after the rear-drivers here, the Audi's step-off is at times absolutely stunning. Sit at a junction in the RS6 waiting for a gap, tum-te-tum. See one, plant the throttle and BAM! With the help of 4wd, the accelerator lives up to its name, thumping the RS6 forward so firmly and instantly that you half expect to hear a metallic crunch and the tinkle of broken glass from the Transit van that just ploughed into the back of you at 30mph.
Even before your first experience of total traction, you know that the RS6 takes its role of high-performance executive transport more seriously than the E55. Everything about the Audi is hard-edged, from the Recaro seats to the steering to the ride to the performance and even the keen down-shifting of its auto box as you coast down - this is a car that means business.
The further you drive it, however, the more you feel that its primary business is more Merc-like than BMW-like, which is to say going very quickly in straight lines. There is more precision to the Audi's responses than the Merc's and traction is very rarely an issue but it lacks the detail feedback and poise sensitivity that allows you to get involved with the process of driving a road like an M5 does. Wind on lock and the RS6's steering goes rather lifeless just when you want more feel, and as the cornering loads build you notice the seat's lack of shoulder support. Grip and traction are still there in abundance... probably. And that's the problem if you're a real driver - you'd rather feel exactly how much there was and be able to go as close to the edge as you wanted to in a given situation, rather than place your faith in the systems.
Sure, the RS6 will do things that the M5 won't. It will find traction, exploit it, and leave the BMW floundering (Merc too, of course) but that doesn't make it a better driver's car. There's no real depth to the experience - when you're not going very quickly, there isn't much to enjoy, and when you are, you don't feel involved. The RS6 is a device that gets the job done, not an instrument that relies on your skill to perform.
What is 'enough power' for the road? Everyone has their own idea, and in this class, with rear-drive, I don't think the M5 is far off it. In the right circumstances, the E55 feels sensationally faster which, of course, is its own buzz and has an undeniable appeal. As we said at the outset, its extraordinary pace redefines the performance saloon: 0-100 in 10.2sec is simply astonishing. Whatever you drive, you'll think twice about messing with an E55 in a straight line, always assuming you spot what it is in the first place.
Yet the M5 has only that to fear. In this class it remains on top because it is the complete package, blending excellent performance with peerless control and precision of chassis, throttle and steering. It would probably struggle to deploy the E55's massive torque and, frankly, it doesn't need it. Sometimes you can have too much of a good thing.
