I wouldn't worry so much about what car to drive.
With some mods, the differences are miniscule; and the AI is horribly "rubber-band"-ish, so it doesn't really matter what you drive -- if you drive 50mph for 5 minutes the AI will let you catch up before the end of the race. Game Designers do that to continue to illusion of a close race. It works against you too. You'll get beat my a Peugot as easy as a Skyline and vice versa.
It's an arcade racing game, not a sim.
