I definately felt the difference in my car at the ROAR nats between mod and 19t. I was using the stock 6 cell chassis, front 5 cells for mod, 6 cells for stock. The mod car was definately more responsive, the 6 cell car was a bit more sluggish in the corners. I never really worried much about the weight of the car before that race, but after feeling the difference firsthand I try to get the weight down now.