Mercedes-McLaren 722 Roadster - Paris motor show news - 2008

The SLR 722 - the powered-up, loudened-up version of the big Mercedes-McLaren supercar - makes, quite simply, one of the maddest noises of any car we've ever tested.

So how's this going to sound? This is the 722 Roadster, the inevitable chop-top version of the SLR, replete with 650bhp 5.5-litre V8 and an exhaust system that makes a Metallica stadium gig sound a bit hushed.

It's an evocative thought, isn't it - blasting down a derestricted autobahn, roof down, speedometer tickling 200mph...

Yep, 200mph - that's what the 722 Roadster will do with the roof down. We're not even sure what happens to cabin aerodynamics at that speed, but suffice to say it'd be wise to put your passport safely in the glove compartment before you set off.

It should be a fairly stable ride even at 220.6mph - that's the curiously precise top speed of the 722 Roadster when the roof's up - thanks to a ride dropped 10mm from the standard, boring, see-'em-every-day SLR Roadster.

We're not exactly sure why the 722 Roadster on the Merc stand has got the roof up instead of down, but as you can see, it's a pleasantly low-key fabric affair. We approve.

If you're keen to find out exactly what happens to your immaculately combed barnet when you hit the double-ton with the roof down, be quick - Merc is building a mere 150 SLR 722 Roadsters.

They'll be on sale early next year. Plenty of time to buy a set of hair clippers.