That's the underskin stuff. The facelift you will have noticed for yourself. And if ever the word facelift was apt, it's here. The headlamps' pinned-back perma-surprised look, the widened grille's eerie rictus, the flattened forehead - all have the aspect of someone who has their cosmetic surgeon on speed-dial.

No, I prefer the elegance of the old face. But I can see why they've done it. All Mercs are going for a harder-edged, more aggressive look. See it in the CL and the C and the new GLK and CLC, and see it soon in the next CLK and E-Class. Trouble is, with the CLC and now the SL, they've grafted a square face onto rounded flanks, and it sits uneasily.

On top of the standard SL facelift, AMG has done its own work, including a unique bonnet (the standard SL now gets twin power bulges). The AMG front and rear bumpers have blackened centre sections that invoke a racing car's aero devices - but only in the visual sense, for the diffuser gives you not an ounce less lift.

Still, because AMG's special front and rear bumpers are so edgy, they go some way to disguising the curviness of the car beneath, so the AMG is the most successful-looking car in the new SL range. Given the AMG has to go toe-to-toe with metal such as the DB9 Volante, the XKR convertible and the 911 convertible, looking awesome is a prime requirement. And it's not quite there.

The SL63 is also the most successful of the new SLs to drive. But once again, some of the opposition is all but insurmountable. I'd take it over the Aston, and probably over an M6 convertible. But versus a 911 or a XKR? Sorry, but with them around, the AMG can't be pegged far above class average.

On top of that, the SL63 has some pretty desperate sibling rivalry to contend with. First off, that superseded SL55 AMG puts up a strong fight. It had as much power and more torque. And what a noise that supercharged lump made! Maybe not so subtle as the 63, but something to put dents in your memory, and your skull come to that. In the 63, you go for revs, and you can drive it with more finesse, but when there's a sudden change to overtake, the sledgehammer kick of the 55 has gone MIA.

Besides, you won't have to go far to find someone who thinks the old car is the more elegant.

The SL63's other problem is that within the year there'll be a Black Series from AMG. The engineers are putting it on an athlete's diet. It will have a carbon-fibre fixed roof, a carbon-fibre bonnet, and seats that are far lighter than the multi-adjustable pulsating electric fat-bum thrones on the SL63. If the engineers get their way, the heavy - and power-sapping - active suspension will give way to a conventional if loony-hardcore steel-sprung set-up. That will save 10-15 per cent of the weight of the car.

Then there's the question of power. It's possible the Black Series won't get more than the SL63, because it costs a lot to put a new version through the emissions and economy tests.

Anyway it'll still have more performance thanks to the weight cut. But AMG people make no great secret of the fact that they can easily find an extra 50-80bhp by straightforward tuning measures like better exhausts. That sounds like a proper supercar, the car the SL63 isn't quite. Won't be cheap, mind.

So let's not give too much ofa kicking to the SL63. It's fast, easy, and fun... and still an SL in that it's a proper Mercedes. Sensible, practical, safe as houses and many times more luxurious than a house - than my house at least. It's also as happy going slowly as it is going fast.

I know this because for the final 40 miles of my drive I was pussyfooting, balancing distance to destination on the navigation against distance to empty on the computer, traversing bleak highlands bereft of fuel stations.

And then with 30 miles to go the distance to empty abruptly cut to zero and I ran on fumes and pure faith.

But it got me there. Trust, after all, is what Mercs are all about.

Paul Horrell