Are you going to use it for Rally? If so, I've found that not going over board with the turbo kits makes all the dif in the world when it comes to drving pretty much all of the rally cars. They handel pretty nice as is IMHO. Remember that hitting the gas in this game has far more impact then it did in previous versions... as a result, if you gun it with full turbo, you're car, or jeepthingy will go all over the place...
If on the other hand, you're looking at using it for street use, try dropping the ride hight... usualy about 5-10 inches from the lowest settings, stiffen the suspention by about 5-6 full numbers and you should pretty much have it down pat. Sorry I don't have actual numbers for you on this thing, I'm still racing with the Subaru Concept. But I've found that these two setting changes have worked pretty well for me any time I use a rally for street.