I say the Minolta is the fastest, but she`s hard to fully control. The Sauber is at a very close second place, also not easy to control.
After that, for me, there are 3 cars:
Nissan R89C Race Car '89: this one grips best. I believe with this car i will get the most constant lap times.
Audi R8 Race Car '01: great to control, very fast, smooth driving.
Nissan R92C. She has almost too much hp, on tracks like Trial Mountain and Deep Forest you will drift more. Very powerfull though.
I prefer the Nissan R89C Race Car '89 out of these heavy weight LMP / Group C Cars.
I think the Bentley Speed 8 is the best if you`re new to these kind of cars. Great to get used to the speed of these monsters. But this is one of the light weight cars. Another example of a light weight is the Mazda 787B.
And by light weight i mean it cannot compete with a heavy hitter like the Minolta.
Just check Stormbringer`s thread, all you need to know is written there 👍