My head hurts. And that's OK, you know. Yes we all know Mercedes are meant to be relaxing, loping long-distance cars, and all I've done is drive a Mercedes for 180 miles. But let's just look at the circumstances. In that 180 miles through southern-French mountains and gorges, the fuel tank has completely drained itself. I've done 10mpg.

So my neck muscles are tired from fighting every whichway; my ears drummed by the awesome thapp-thrappa-thrappa-bu-bu-bubb of the V8 rattling its sonic reflection off the rock faces as it accelerated and lift-off-backfired through the hills. I kept the roof down to better get the full head-in-the-bass-bins effect - hence the pummeling of wind around my upper body. Result of all that is the headache.

An ailment I want to repeat, please. Pretty please.

I once did a similar drive in an SLR and all I got was a stress headache. The SLR is feral and uncommunicative, and it left me a bit of a gibbering wreck. The SL63 has nowhere near the SLR's raw performance, but I'll bet I was as fast through the corners this morning because the SL63 makes me feel so much more confident and joyously alive.

I always was a fan of AMG's SL55. It's gone now, replaced by the SL63. There's no supercharger here, but the wild 6.3 engine (OK, actually 6208cc) makes good. It also gets an all-new method of transmitting the power between engine and transmission. Oh yes, here we have yet another kind of flappy-paddle device... but it's a good one.

The heart of the Speedshift MCT is Mercedes' seven-speed autobox. Because it's an auto it shifts without a pause, which makes it fundamentally different from sequentially activated manual devices from Ferrari et al - they have to go through neutral. Normally, for starting off and for cushioning the shifts, an auto box has a hydraulic torque converter. Trouble is that's heavy and blurs the sense of connection from throttle to wheels.

So the new AMG box does without the torque converter and instead has a multi-plate clutch, programmed to open progressively when you're starting or stopping, and to give a moment of slip to cushion gearchanges. It's the programming of that slip which has defeated previous attempts by others to do the same thing, AMG engineers smugly imply.

How much slip depends on what you select on a rotary knob. 'C' for comfort makes it slur the shifts like an old-school auto, but go through 'S' to 'S+' and finally 'M' for manual and you get ultra-fast (in fact sometimes fast-beyond-smooth) paddle-requested changes, a nice blip on downshifts and a real sense that the engine has been relieved of a heavy flywheel and just wants a tickle of the throttle to bark up through the revs. And if it wants, well who am I to deny it?

The SL's other technical highlight is kept on: the active Body Control suspension, which uses hydraulic legs to do the work of springs. It means the car doesn't pitch or roll, and because the virtual roll-stiffness is varied front-to-rear according to your speed, you get turn-in oversteer in slow bends so it feels agile, and understeer on fast bends so it feels stable.

Sounds like off-putting techno-voodoo, and on some Mercedes it is, but here it actually feels pretty natural while performing the minor miracle of making this two-tonne cruiser dance more-or-less like a sports car. And it does do a fairly good job of disguising the weight. Not quite as good as being without some of the weight, as a drive in a Jaguar XKR will confirm, but a good job anyway.

Normal facelift SLs get Mercedes' 'direct steering', a rack that gets sharper the more lock you apply. It means you don't have to do much wheel-twirling in town or hairpins, but it also has an odd patch half-way into a corner when it's very unprogressive. So AMG binned it and now uses its own quick but constant-ratio rack. It's nice and predictable and also has a useful bit of feel. Definitely an improvement.

These days any supercar without multiple driver-adjustable parameters is going to get bullied in the playground. So the SL63 has an array of buttons and a little wheel. Between them they allow two suspension modes (in practice little different), four transmission modes, three ESP modes and a launch control. The intermediate ESP 'sport' is brilliant, giving you a properly lively tail while saving you from yourself. The 'off' setting means it.