Having raced both locally, with the same car, I can tell you that a good set-up is very different between the two. YMMV, but I couldn't just slap VTA tires and shell on my GT chassis and go out there and make fast laps, and vice versa. I have aquired two chassis in order to run both classes. That is just my experience... I find the set up (camber, spring rates, ect) to be very different (to get the car to run at the front of the pack) in each class.