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Ditto for the route's two most famous mountain passes, the Futa and Raticosa between Florence and Bologna. Moss did those 60 miles in 61 minutes; at just 60mph a slow section for him, but to the rest of us that would be speed to the point of delirium.

No, the interesting leg is through Lazio and Umbria. I start on the outskirts of Rome, end at Siena. The route in 1955 was actually simple. There weren't any motorways, so they used the old national network, roads with evocative names rather than numbers. Via Emilia, via Aurelia, via Salaria, via Flaminia. And for me today, all the way on the via Cassia.

To begin with I'm bottled up through interminable suburbs. A healthy jogger could beat our first 20 minutes. The SLR doesn't care much for it either. Never mind the automatic 'box, leather-lined cab, electric seats and steering column, climate and telematics, it still feels like a thinly draped race car.

A Bugatti Veyron is better tamed in traffic. So's a 599; the SLR in many ways feels more like a Carrera GT. The McMerc's super-rigid carbon tub creaks and bangs, and the electronically controlled carbon brakes have horrible low-speed modulation. They're either on or off, and the pedal has no feel.

The steering is heavy and equally dead. The engine rumbles and zizzes a little. The car's width is a problem, though not an insurmountable one because visibility itself is fine.

Oh, but it makes the school kids' day. This one is painted dark grey but any SLR has such immense presence, it's a shaft of light in the dreary traffic. Yet oddly the SLR has slipped out of the general petrolhead consciousness since it launched.

Doubters say it's just an expensive SL55. But seeing one and being in one gives lie to the notion. Its presence is one thing that's on a wholly different level from the SL. Its performance, its entire feel and animus, is another.

Towards Viterbo I'm beginning to get an idea of how. There are odd gaps in the traffic. The SLR is a sledgehammer of an overtaker. There are just five speeds, but with 575lb ft of torque from 3,250-5,000rpm, you hardly need more. Kick it down or use the responsive little paddles and there are times when the traction control flickers even at 70-plus. And that's even going in a straight line.

The mighty V8 rumbles deep like NASCAR, then when the supercharger kicks in there's an overlaid scream that fair terrifies you the first time. Then wind down the window for an extra twist: hissing pulses of exhaust from the storm drain side-pipes.

I keep shifting up at 6,000-odd, forgetting it'll run to seven. You'd need an autobahn or a track to consistently make use of that top-end, never mind the extra ponies of the 722. Then it's a distant dream, as I'm stuck in traffic for an hour.

Just north of Lake Bolsena, I go through a whole little town at 30mph with no one in front of me. Opening up ahead is some of Europe's best driving country. The view is clear, not only of one of the planet's loveliest landscapes but also of the road as it snakes away.

The topography is rumpled like an unmade bed, the road often changing direction in all three dimensions at once. The SLR's performance compresses it, turning what look like straights into bends, sharpening each corner and bringing it closer to the last.

And the SLR eats corners. The V8 sits behind the axle line, so it turns instantly like a mid-engined car, though you experience it differently because your vantage point is so far aft. There is never the sensation of running wide at the front; the only commotion is at the battle of the titans down at the rear contact patches; vast traction versus all that torque.

The suspension's long travel is beautifully judged, the hard town ride morphing at speed into something that'll allow the tyres to follow the convolutions of these road surfaces. You feel it as traction and especially under the violence of hard braking, where the stopping is so true you feel calm enough to glance in the mirror and see the air brake pop up.