As we accelerated through 100mph I tried to touch the dashboard — just for a laugh. By the time I had summoned the strength to execute this apparently simple task we were doing 130mph. People who test cars are fond of describing how the acceleration of one quick car or another pinned them to their seat, and you know as well as they that they don’t actually mean it, it’s simply a figure of speech. Not in this Mercedes it isn’t.

The Mercedes CL65 AMG not only has 612bhp — just 15 short of the McLaren F1, still the world’s fastest car — it has 738 lb ft of torque, a figure no production car in history has ever approached.

But this is only the start of the silliness. Would you believe that these figures are actually artificially restricted and that were this 6 litre twin-turbo V12 engine really let off the leash it would generate more than 880 lb ft of torque and 700bhp? You’d better because the sole reason for the restriction is that if it were left to its own devices it would melt its gearbox.

The price paid for such insanity by the 20 or so British buyers who will find themselves behind the wheel of a CL65 next year will be between £120,000 and £130,000, and if that doesn’t get your heart bleeding for them, perhaps it should.

Being in the market for a car such as this must be hell. So far as I can make out, the only possible motive for wanting one is some gnawing doubt that someone else might have something more powerful.

Pity the poor soul, then, who two years ago bought a brand new top of the range 408bhp CL600. They’d have felt pretty pleased until Mercedes popped a couple of turbos on and bumped up output to 500bhp. So they buy the new full-fat CL600 when blow me if AMG doesn’t go and do its own version — this car — and up the ante to over 600bhp.

With wallet bleeding they slap down their order, convinced that now they will be the fastest of all. What odds would you give on their dealer then mentioning the new seven-speed gearbox that Mercedes will install in this car next year, allowing its thereafter unfettered engine to produce the full 700bhp? They will wonder where it will all end, and if they have any sense conclude bankruptcy or the nut house.

Yet, on one level at least, the CL65 is a beguiling car, not so much for how it behaves when you go fast but for its nature when you don’t. If it wasn’t limited to 155mph this car would have a top speed of 208mph. ()

However, when you fire it up and use it for going about your daily business it is no less civilised or refined than the S-class limousine upon which it is based. You could drive your grandparents in it all day without them twigging they were in a car with more power than every roadgoing Ferrari ever made (save the Enzo). That 208mph top speed is the same as is claimed for the McLaren-Mercedes SLR, yet the CL65 will seat four in comfort, cruise in silence and cost half the price.

But unlike the last two AMG cars I’ve driven — the superlative E55 and SL55 — this was not a car I ultimately warmed to. The engine has so much power it asks questions the rest of the car can’t answer. Despite a revised chassis and still bigger brakes, it corners and slows with nothing like the assurance with which it accelerates. It may be mighty fast in a straight line — Mercedes says 0-62mph in 4.4sec — but its roadholding is disproportionately modest by comparison and its steering rather too vague. Once the novelty of its sheer thrust wears off, what remains is simply not that much fun to drive.

Mercedes says the CL65 is a car built to answer demand from its customers, which is no doubt true. But I suspect there is another reason. I think the true purpose of all that performance is not to allow a Mercedes to cover the ground quicker than anything else, but to impress upon the world that when it comes to power, acceleration and theoretical top speed, no rival comes close. And with Bentley sitting on several thousand orders for its cheaper 552bhp, 198mph Continental GT, you can see why Mercedes feels it’s a point it has to make.

Whether that makes the CL65 a car worth having is another matter. The problem with power is that however much you have of it you get used to it. And once this happens what remains is too little advanced over the standard CL to significantly elevate the driving experience.

So if you drive a CL600 with merely 408bhp, or even 500bhp, and were pondering spending what will probably be at least another £30,000 on the 612bhp CL65, save yourself the money. At least until next year, when its power seems destined to top 700bhp. Then you’ll be able to say you drive the most powerful production car ever sold.

VITAL STATISTICS

Model: Mercedes-Benz CL65 AMG
Engine type: V12, 5980cc
Power/Torque: 612bhp @ 4800rpm / 738 lb ft @ 2000rpm
Transmission: Five-speed automatic, rear-wheel drive
Suspension: (front) Four-link, air springs, anti-roll bar (rear) multilink rear axle, air springs, anti-roll bar
Fuel/CO2: 19mpg (combined) / 357g/km
Acceleration: 0-62mph: 4.4sec
Top speed: 155mph (electronically limited)
Price: £125,000 approx
Verdict: Impressive on paper, disappointing on the road