Look at the Le Mans series racers, none are running nothing >300. By moving the springs in 3" and the wider tires allows for great contact with the ground (very important), however if you don't want the to move the springs in you can always flare out the wheel housing area to get wider tires.
As far as the auto I used was an amatuer day at the track and I did it in a caddi cts (great riding car) I came in second and the only car to beat me (out of 16 on the track) was a viper designed for road racing.
