Let's break this down in as logical a way as possible. The Mercedes Benz SL55 AMG retails at £99,045. Its 517bhp power output puts it amongst some fully fledged supercars and independent test have shown that a derestricted version will thrash cars like the Lamborghini Murcielago and the Porsche 911 GT2 to 300km/h. It's an apocalyptically quick car by virtually any measure. The thing is, AMG don't like the word 'virtually'. This is a company that deals in absolutes and with the SL65 AMG, Mercedes' high performance arm have created a car that revels in its excess.

Take the price. At £148,955, the SL65 AMG is £49,910 more expensive than its SL55 AMG sibling. To put that figure into perspective, that's a Mercedes S350 on top and that premium is ostensibly for a bigger engine. Think about it. If an SL350 retails at about £63,000 and, being charitable, £20,000 of that is being spent on engine, the SL package minus powerplant is in the ballpark of £43,000. That would seem to make the engine fitted to the SL65 AMG worth around £90,000 taking into account the extra trim items in the cabin.

But what an engine. With 612bhp on tap and a torque figure of a cool 1000Nm, this twin turbocharged V12 powerplant has the capacity to redefine your benchmarks for retina-detaching acceleration. Hand built in Affalterbach at AMG's facility, this 6.0-litre behemoth won the 'Best Performance Engine' title at the International Engine of the Year Awards in 2004, beating off over 70 other contenders. True to the philosophy of 'one man, one engine', each unit is fully assembled by its own AMG engineer who is responsible for the entire procedure: installing the crank case in the engine block, fitting the camshafts and the turbochargers, routing the wiring and even topping up the engine oil. The engineer's signature is visible on an engine badge. At least you know on whom part of your money is being spent.

"AMG are a company that deal in absolutes"

So much for the background. You want to know what happens when you attempt to stomp the accelerator pedal through the bulkhead. Believe it or not, the first sensation is mild disappointment. The turbochargers take a while to spool up, but the torque quickly overwhelms traction at the back and the first few tenths of a second are spent watching the traction control lights blink frantically as you wonder what all the fuss is about. Realisation hits you rather rapidly. As the huge rear tyres claw desperately at the blacktop, the turbochargers get their act together and begin to go to work. The effect is concussive, the big Mercedes lunging forward. It feels like the car is trying to concertina in a cartoon fashion as you're pinned to the seat. In most quick cars, this experience lasts a second or so before the onslaught subsides and you grab for another gear. Not so the SL65 AMG.

The AMG Speedshift automatic transmission allows the engine's torque to keep pouring back to the rear wheels in a seemingly uninterrupted torrent. The dials start to read ridiculous velocities and you begin to wonder quite how good the brakes are. Huge 390mm front and 360mm diameter rear composite brake discs do a valiant job at hauling the SL65 AMG down from speed but despite their efficiency, it's impossible to escape the sneaking suspicion that engine technology has, in this instance at least, somewhat outstripped brake and tyre capacity.

The roof mechanism of all current generation SL models is slick, lifting or lowering in a mere 16 seconds. When opened or closed, the rear screen rotates to reduce the amount of boot space the folded roof impinges upon. On the downside, the 11 hydraulic cylinders utilised help the SL to a hefty kerb weight of 2110kg; a fair bit heavier than even a long-wheelbase S-class limousine.

Mercedes has gone to great lengths not only to make this model safer, cleverer, quicker and cleaner than its predecessor but also to improve the dynamics. The SL was never a car that would look upon a corner with any great relish but the latest model has not only shed weight - due in no small part to extensive usage of aluminium body panels - but also features the astonishing automatic body control (ABC) system used to such devastating effect in the behemoth Mercedes CL coupe. Put simply, the Mercedes SL doesn't roll through corners yet does without the attendant bone shaking ride quality you'd expect from such a taut handling car. This is due to a set of electro hydraulics that lower the ride height when the 'Sport' button is jabbed.

The cabin can be specified with either wood or aluminium trim detailing in conjunction with the leather upholstery. Electrically heated and adjustable AMG sports seats with fluting and perforation provide a decent compromise between armchair comfort and bucket seat support. The AMG instrument cluster is trimmed in Alcantara and schoolboys will coo in astonishment at the speedometer that reads to 225mph. An AMG sports steering wheel with gearshift buttons is also featured, as are aluminium etched door sill panels, bi-xenon headlights and the COMAND information and control system which includes satellite navigation and a CD multichanger. As it should when you're forking out this sort of money.

Although from the outside they may appear ostensibly similar cars, the SL65 AMG appeals to a very different customer to its SL55 AMG sibling. Whereas the '55' is something of a performance bargain, offering Lamborghini speed for far less, the SL65 AMG can only really be recommended to those for whom the price tag stopped being a consideration some time ago. It's mad, excessive and stRangely addictive, but as great as that engine is, much of the same experience is offered elsewhere in the Mercedes line up.