Most of the setup parameters have little, if any, effect on lap times. Set tire pressures low, boost and nitrous high, (cam timing doesn't do much) and adjust gears if needed.
For a grip car, if you want points, use the 911 Turbo, if you want fast lap times, use the Zonda. The Ford GT is next fastest, but difficult to drive. Then the 911 Turbo, and then the Mazda RX8, which is probably the best car to use as a starter car. Here is a walkthough that includes recommend cars and the setups:http://rcgldr.net/nfsp/nfspwt.txt