Just back from France after a couple of successful track days. I took advice from a couple of racers and the race instructor to leave the tyre pressures as advised by Audi. The car worked a treat and surprised a lot of the other cars - lots of Porsches, Lotuses, 3 GT40s and a couple of M3s. In the wet the traction was a real winner and very few could stay near me out of the tighter corners. In the dry it still performed very well. After about 6 laps (3.4 km per lap) the tyres were cooked and turned to 'chewing gum' - but they recovered fine for the drive home.
Brakes were very impressive, no fade at all. This would probably be different with track tyres fitted, but with road tyres it's the tyres that give up first.
Fastest car there - probably the Audi A8, but a toss up with the full race spec. Porsche RS4 and the Ultima. There was a Nissan GTR there, but the driver was pretty slow.