A little more than half a century ago, at 7.22am on May 1 1955, Stirling Moss left the start line of the Mille Miglia road race. Without the help of motorways and despite crossing a mountain range, just over 10 hours later he was back, having put nearly 1,000 miles under the spoked wheels of his Mercedes-Benz 300 SLR.

Nobody had done it so fast and nobody did so again. Moss’s win is the most famous of any by a Mercedes, and his car, still owned by the factory, is believed to be the most valuable in the world.

Why am I telling you this? Because the number on the side of the Mille Miglia cars correlated to the time it left the start line, which is why Moss’s number was 722 and why, more than 50 years later, Mercedes has put it on the side of another car. The result is the Mercedes-Benz SLR McLaren 722 Edition, which costs £340,000, £22,390 more than the standard SLR.

It is designed to appeal to those for whom the normal SLR power output of 626bhp is not quite sufficient. With a bit of electronic trickery, the 722’s motor has been tickled up to 650bhp, making it more powerful even than the only other production road car to wear a McLaren badge, the unforgettable F1. It’s lighter than the basic SLR, too, better braked and derives more grip not merely from its lowered, stiffened suspension but aerodynamically, thanks to a new front spoiler that increases the air pressure on the nose of the car at 150mph by a staggering 128%. And, as if it matters, its top speed rises 2mph to 210mph.

Even in the wide open spaces of the deserts of Oman and Dubai where I drove it, it feels science-fiction fast. When 170mph is just the nudge of a toe away, the challenge is not to see how fast you can go but how slowly. You might regard a car that can reach 60mph in less than 10sec as pleasantly swift — but give such time to this SLR and you’ll see the dark side of 120mph. It doesn’t howl and scream at you, as will a Ferrari 599 GTB, it roars and bellows instead as its supercharged 5.5 litre V8 motor clubs you up the road. It is a brutal, physically and mentally draining experience. And it’s just great.

But the more I drove it the more I realised this is a car that doesn’t know its station in life. On one hand it appears to want to be the ultimate high-speed touring machine: at a constant cruise it’s reasonably refined, the boot is big and it even has a nice and easy automatic gearbox.

Why, then, fit stiffened suspension that wrecks the ride quality? Why give it ultra-aggressive steering that makes it change direction like a racing car when the only effect this has on the public road is to make the car feel needlessly nervous?

And while I applaud the desire to fit brakes strong enough to reverse the Earth’s rotation, I don’t understand why they need a dead feel that’s disconcerting when you’re trying hard, and plain annoying in traffic. Ferrari and Porsche have similar systems on cars costing a fraction of this and they work just fine.

The idea behind the SLR was that it should provide the performance of an ultra-specialised supercar such as a Ferrari Enzo or a Porsche Carrera GT but in a package sufficiently civilised that owners would not be afraid to use it. I first drove it in 2003 and while it was undoubtedly a flawed product it hit this target with reasonable accuracy. By contrast the 722 has the performance but has lost the civility, without gaining the heart-stopping thrill of an Enzo.

Or, as can now be said, a Ferrari 599 GTB. The fact that Ferrari last year produced its greatest car in the past two decades makes me ponder the point of this SLR. The Ferrari is 0.1sec slower to 62mph and has a top speed 5mph lower. But I drove the 599 on roads 10 times tougher than those provided for the SLR and it coped with imperious ease, while simultaneously supplying one of the greatest drives of my life. And here’s the killer: at £171,825, the Ferrari is just a smidgeon more than half the price. Yes it’s made from aluminium rather than exotic carbon fibre like the SLR, but it is the result rather than how it is arrived at that interests me.

Not that this will bother Mercedes. Only 150 of these SLRs will be built and those destined for Britain have been sold. Mercedes is now turning its attention to the convertible SLR Roadster that will be shown this summer. Lacking the strange modifications that spoil the 722 but with a retractable roof and — probably — the 650bhp engine, I suspect it will suit the character of the SLR more. It will also find favour among customers who will want to make damn sure everyone knows who’s just spent a third of a mill on a car.

I suspect it will succeed like no other SLR before it, unless of course you count the one used by Moss to win the greatest race of his life.

VITAL STATISTICS

Model M-B SLR McLaren 722

Engine type 5439cc, eight cylinders

Power/Torque 641bhp / 604 lb ft

Transmission Five-speed automatic

Fuel/CO2 n/a

0-62mph/Top speed 3.6sec 210mph

Price £340,000

Verdict Ferrari does it better

Rating 3/5

Date of release Already sold out

The opposition

Model Ferrari 599GTB

For Best Ferrari in 20 years

Against Dubious looks

Model Lambo Murciélago

For Shatteringly quick

Against Difficult in traffic