A guy in our 4300 class is running his with a sphere, and for some reason, it stopped going into thermal shutdown. I think he kept weakening the magnets in the rotor, and then kept gearing it up. He was fast as hell in the main, and then slowed way down and pulled off toward the end. He temped the motor at... 253 degrees. Ouch.
It seems like maybe as the magnets get weaker, the RPMs go up, but also the motor gets hot faster. I'm not positive, but we're having mixed results with rollout and temperature.
I decided to gear my 4300 w/sintered rotor until it started warming up, and it started getting faster finally. I think my rollout was around 32mm in the main tonight, and the motor came off at 128. It finally felt like I was close in speed to the other guys, though still a bit behind. The two guys in front of me both thermaled/overheated in the last minute and I got the win. Woo. :-D