Unfortunately we haven't done a huge amount of testing so far because our FRC team decided to go with a different drive system this year. I fatigue on the belt is directly related to the load on the belt (pre-load plus dynamic load). Both of these can be minimize if the mass of the robot being driven is lowered. My gut feeling, though, is that for an FRC competition robot, which only gets run for a few hours to 10's of hours total, belt failure will not be a problem, and if there is the occasional belt failure, they are easy (and relatively cheap) to replace. The bigger limitation is the torque that can be delivered through the relatively tiny 6mm wide, 3mm pitch belt before the teeth start to skip on the small pulley.