Mercedes-Benz SL500 Roadster

Price: £83,455
Engine capacity: 4.7-litre twin turbo V8
Power output (BHP@rpm): 429 @ 5,250
Top speed (mph): 155 (limited)
0-62 mph (seconds): 4.6
Fuel economy (mpg): 31.0
CO2 emissions (g/km): 212

It can be a risky business planning a weekend away in a convertible in September. To bask in the heat of an Indian summer with the roof down or sit cramped with the roof up as rain hammers down? If we're honest, it's a risk convertible drivers face all summer long in Britain, one that, along with the recession, is probably why top-down sales have dropped almost 50 per cent since 2007.

At just over £83,000 the new Mercedes SL500 won't be the car to reverse that sales slide. It will, however, for the lucky few, go some way to taking the wet-weather risk out of open-top motoring. It's only the sixth-generation SL since the company launched its grand tourer in 1954 and aims, as ever, to offer the world's wealthy the exhilaration of open-top sports performance with all the luxury (lots and lots) that Mercedes-Benz can muster.

It does this in part with a proper hard-top roof that folds out in 20 seconds and turns the SL from a convertible for summer into a coupé for the other 11 miserable months of year. The SL500, the most powerful SL before the bonkers AMG Sports version, also gets a 4.7-litre twin-turbo engine to push this contraption, plus matte paint, luxury-leather heated seats and bags of gadgets, to 60mph in just 4.6 seconds. Make no mistake, the SL500 might boast a proper roof and a clever gadget to keep your neck warm as you storm along with the roof down far too late in the year, but it's not soft. It's seriously fast.

To test this blend of unaffordable but wonderful luxury and top-end performance, I head north for a 700-mile round-trip to the Lakes. I made the same run earlier this year in a high-spec BMW-3 Series and the first shock is that the SL500 is just as comfortable (if not more so, thanks to its air suspension) as the luxury saloon. The ride is silky smooth and there's practically no wind or tyre noise on the motorway. Of course you should expect this for the money, but it is still impressive that the car has turned a two-seater bruiser of a sports car into something that wafts along with such ease. The fuel economy doesn't disappoint either as Mercedes has worked hard to make the SL 140kg lighter than the model it replaces by using an aluminium construction.

This cruising luxury and new-found efficiency is all well and good, but it's on the B-roads of Britain that the SL500 is really at home. First off, this isn't a car designed for raw driving pleasure – opt for a Porsche 911 or Jaguar XK if that is your thing – instead it's for progressing rapidly, yes, but for doing it in style with the top down. And with the sun out last weekend it did this very well indeed. It's composed, calm and perfect for covering miles quickly with a minimum of fuss. And if the mood does take you, it is only a click of a reassuringly chunky and expensive switch to engage manual mode, drop a gear and unleash some of its 429 horses to overtake (or show off) with ease.

Perhaps the engine note is not brash enough and the steering is a little light, but it's pretty and people will look at you. That, I suspect, is just what its owners will want, because if you can afford a car like this, you don't really need to be driving fast to show it off. You just need a little sunshine.