Ok, my son started out with the 4200 in his stampede and stripped the idler gear within the 1st minute of running it. So, I put the same pack in my rustler with a 14 turn motor, 17 tooth pinion, and 84 tooth spur and continued adding on to the time already put on the battery in the stampede with my son still driving. It ran 15 minutes before there was a noticeable power drop. By 16 minutes and 30 seconds it was slow enough for me to call it quits. This was pretty much full throttle the entire time.
Hope this helps.