A boost in power ruins the Mercedes SLK formula

Oh, this little Merc has it, but Kevin Hackett finds the added oomph ruins the formula.

The SLK 55 AMG comes with a retractable folding glass roof that darkens electronically and black wheels that, unfortunately, do not lighten up.

When I drove the new SLK 350 in Tenerife early last year, I was full of positive appreciation for how Mercedes-Benz had cleverly turned what was, essentially, a car that appealed to women, into a more manly plaything. It was a superb blend of grunt, sophistication and fun. Surely, I reasoned, when the inevitable AMG model arrived, it would be even better. I was wrong.

Having been bowled over by other AMG models in recent months, the SLK stands as a shining example of how power can spoil a recipe that had nothing wrong with it in the first place, and that's not something I say lightly. Because for petrolheads the world over, more power almost always guarantees more fun and more excitement. The SLK 55 AMG has, by becoming more powerful, emerged as something of a blunt instrument - a lump hammer instead of a surgeon's scalpel.

The 5.5L V8 under the SLK's bonnet had potential to give this diminutive sports car a real edge. In other mad Mercs, the AMG treatment has resulted in massive dollops of machismo, sounding thunderous and hurtling occupants down any given road in a blazing trail of glory. Not so here. It's too quiet for starters, offering a muted thrum instead of a guttural bellow.

And there are unhappy compromises elsewhere, too. The suspension is stiff - too stiff for a cross-country dash. The compliant ride of the lower-powered models in the range has been sacrificed for "sportiness" and it doesn't suit the car's more relaxed approach to fast driving. It's not often that Mrs H says she'd rather get out and walk when I'm driving her on the Sheikh Zayed Road in Dubai and that, for me, would be a deal breaker. Often, when you're driving, you're not aware of how stiffly sprung a car actually is - a passenger will soon start complaining, however, which is hardly ideal when you're supposed to be enjoying a day out together. If you happen to be inside a supercar, a stiff ride comes as standard (unless it's a McLaren MP4-12C) but the SLK is another animal entirely.

The interior is quite lovely, however, and the glass roof that changes from clear to dark blue at the touch of a button never fails to entertain. It's pretty effective at blocking out the UAE's summer sun, too, so it's far from being a useless gimmick. When that roof is lowered, however, it does render the boot fairly useless. The dashboard is well designed, with a minimalist approach to buttons and switches, and there's a feeling of robustness and longevity to everything you touch. Merc interiors are among the most tactile anywhere - a far cry from the usual mass-produced motors' cost cutting.

Going back to that engine for a second, the big V8 features cylinder deactivation in the name of economy and planet saving. Unlike other cars that feature this remarkable technology, the SLK falls back into blunt mode when the engine switches between four and eight cylinders, causing you to feel a bit of a thump when it should be totally imperceptible. The eco tech goes further, too, with stop/start functionality that can be a bit embarrassing at the lights, causing onlookers to think you don't know how to drive, so it's best left switched off, which kind of makes it irrelevant. This is never going to be a car embraced by eco-warriors - if you're a motorist with a conscience you won't be putting down a deposit on anything with an AMG badge on its flanks.

Find a straight, empty road, and give the lump hammer some exercise, and there's no shortage of blistering pace. With 415hp at its disposal, the 100kph dash is dispatched in just 4.5 seconds and the top speed, while limited to 255kph, could be achieved in next to no time. But a sports car should be able to offer thrills on roads with corners and this SLK starts to feel decidedly nervous when you keep the power on through a bend. With no traction up front, the rear tyres feel like they want to tear themselves free from the tarmac with even the slightest flexing of the right foot, and that's with all the electronic safety systems working overtime. Fun to drive hard it certainly is not.

Image wise, this is still a car that suffers from the girly associations and the AMG spec actually makes these more apparent by trying too hard to be macho. The black alloy wheels look out of place and the SLK's short wheelbase is accentuated by the various aerodynamic addenda. It's all a bit confused, no matter where you look, but never more so than when you're behind the wheel.

So if an SLK is the Merc for you, do yourself a favour and keep it (relatively) simple by speccing up a 350. With less power it actually becomes more of a car - more comfortable and more appealing in practically every way.