Great thread, for possibly the best race in GT5.
I did it last weekend, in the Nissat GTR Academy Version. Only did a oil change, and racing filter. Racing hards for rubber. In relation to the other competitors, quite a heavy car.
I didnt encounter the audi r8, though had a good battle with the tuned Audi-TT (the orange one, cant remember what it is called), and the amuse s2000 (non turbo). However, their pit strategy didnt give them any competitive edge, so won with a margin of 4 minutes.
Next, I'm planning on doing it in the Alfa TZ2, then a Ruf (maybe the yellowbird), then a tuned Nissan Silvia Spec-R, since I once read of a guy having a great 200 pts race in GT4 with that. But in GT4, I dont think the competition was as "hard" as in GT5?