We are running a Corally 5.0 star wind on our Gen-x and the rollout has been between 32 - 35 mm depending on the track.

With a 4.5 motor most people seem to start dumping their batteries around 7:40 or so. Only factory sponsored guys seem to have good enough batteries to last the whole 8 minutes. Rollout should propably be in the 30-33 mm region.

Jumping to mod from stock you might want to go with a little bit less power and have a much easier car to drive.