Usually your piston breaks first, are your piston teeth full mental..?
Well, you have to understand the high speed and high torque gears are meant for different reasons.
High speed gears are meant to give an airsoft gun a high ROF while high torque gears are just meant to pull a stronger spring.
So, if you had a M130 spring, I would go with high torque gears, because it would go along with high torque motors and a Li-Poly battery. Anything below M120, high speed should work fine. Just don't hold full auto for 10 seconds. lol.
Here a whole thread
http://www.airsoftcanada.com/showthread.php?t=111990