I think the slicker and smoother the surface of a car, the faster it will go. Alot of the best racers don't even paint their cars in leiu of weight. I have a system that uses waterslides and clear coat laquer that keeps the car at a specific weight. For instance, my Street Pro car (TRISKADEKAPHOBIA) was at a weight of .510 after drilling axle holes, weight pockets then shaping the car. After sealing the body, putting on the waterslide and clear coating & wetsanding & buffing it out plus adding fenders, and DD4H wheels/axles, the car was at a total weight of 1.005 ozs. thus leaving me approximately 4 ozs of weight to put in the car, and that translates to speed. Now, I ain't had the race results that I would like lately, but it's not because my cars have paint on them, I just have been getting beat..fair and square, plain and simple!! But, I have had my cars intentionally running slow so that everyone can see how many times the color shifts in the paint as it passes by the lights(that's a bit of a FIB), all joking aside, it is the builders preference as to do they spend time painting, or time testing and tuning. I would prefer the latter, but I really enjoy making a car look like a piece of candy as well.
Take care,
Spark