For goodness sake, stop this nonsense; 612bhp is already into the outer stratosphere as far as power outputs for road cars are concerned. Yes, the Ferrari Enzo has more. But the CL65 was conceived to be a comfortable, executive express, not some finely honed sports car with rock hard suspension settings. So how does the CL65 cope with this huge wave of power? Well, it does cope, but only just.

Peering out through a porthole (from the ridiculous yacht that Mercedes has chartered for the launch) towards the three CL65 press cars parked beside the Monaco Marina, I'm hard pressed to tell them apart from the current CL55. They even have the same wheels, since their bespoke alloys, as pictured above, weren't ready in time for this event. Look more closely, though, and you see V12 Bi-Turbo badging on both front wings. But the real giveaway to the car's potential are the colossal quad exhausts protruding from under the rear valance that leave you in no doubt there's something very special under the bonnet.

Inside the cabin there are even fewer clues on offer. A quick glance reveals only the numbers on the speedo have changed, the biggest number now reading 360kph (224mph). All pretty pointless, really, as the car is still limited to 155mph (250kph). Even if you pay to have the car 'delimited' then the top speed only nudges up to an electronically governed 186mph (300kph), as that's the highest speed the special Michelin tyres can cope with. Squint a little harder at the dials and you'll notice they've managed to squeeze in another 'Bi-Turbo' script next to the rev counter.

And that's it for the changes inside; the walnut trim remains the same as in the CL600 the car is based on, as do the unsupportive seats and nasty plasticky feel to the rest of the cabin. Mercedes really needs to do better than this to justify the ΂£30-35,000 price premium for such an exclusive model.

Nosing out from the Marina in the CL65 for the first time and, to begin with, there isn't a hint of the potential mayhem the car's capable of, although there is a distinctly aggressive rumble from the quad exhausts that's bouncing off the plate glass windows in this most exclusive of suburbs. The route out of the Principality, towards the hills beyond, takes us through a tunnel carved from the rock that towers above the port. I can't resist a proper prod of the accelerator as we enter the mouth of the deserted tunnel; electronics shuffle us down from fifth to second and in a blink the twin turbos have primed the mighty engine to deliver the full Monty. Even though we're already doing 30mph as we enter the tunnel, the now familiar yellow ASR symbol on the dash is blinking furiously as the electronics struggle to cope with the enormous power being unleashed.

I'm struggling with the noise that's bouncing back off the walls of the tunnel - it's seriously loud, a deep bellow overlaid with a chorus of turbo whistle. There's pulverising acceleration occurring too, the sort that freezes you to the seat and pulls at your neck- muscles while the immediate horizon is hoovered up in front of you. It's relentless too, as the auto slurs-in one cog after another, seemingly without any interruption as the force of 612bhp does its stuff.

It's undeniably impressive. And the extraordinary part is the way this incredible acceleration is so accessible all of the time. Dismissing a troublesome lane-blocker on the autoroute (once they pull over, of course) has never been easier. The only trouble is that you frequently find yourself engaging in a relentless rush for the far distance only to bounce into the speed-limiter. I'd love to find out how fast this car goes from 100 to 150mph, as it feels time-warp fast. All we know is that the dash from 0-124mph is claimed to take a mere 13sec. All normal references are lost within the leather and walnut cabin, with supercar acceleration the merest flex of your ankle away.

Unfortunately, I'm not really enjoying it as much as I should, because the rest of the car struggles to keep pace with the engine. I've set the ABC (Active Body Control) suspension to Sport but it still doesn't seem taut enough to give you the confidence to push the chassis to the limits. Mercedes has changed the front struts for the stronger ones developed for the CL55, but even they struggle to keep the weight of this mighty engine in check. Then there's the brakes, which have the soggy feel of the standard stoppers fitted to the CL55. Odd, when the press pack boasts of composite brakes. Read on, though, and it turns out the actual discs are made of the same cast iron as standard but the carriers they're bolted to are made of a composite alloy that's there to help stop some of the heat sink into the overworked front hubs.

It seems to me there's still work to do with this car. The easy bit was developing the engine; the hard bit is finding a proper home for it. As it stands the CL65 is a bit of a laugh in a straight line, makes a glorious noise under load but is over-engined for the chassis.

The ΂£37K-cheaper CL55 is plenty quick enough to play the hooligan when the mood takes you. No wonder, then, that Mercedes expects to sell only 20 CL65s in the UK next year.