This might hurt!
Using foams on carpet is for whimps! Anyone can drive a car with foams on carpet. (for touring cars that is)
Using rubber tires on carpet will improve your driving skills because you need to get your setup right and drive smooth lines. Its a proven fact that the best drivers here in Europe use only rubber tires on their touring cars.
For pancars its a totaly different story. Here you need to go with foams, but this is due to the fact that these cars go a lot faster then 4wd cars and they are 2wd so you need al the traction you can get.
I'm expecting a lot of respons to this statement, so give it to me