A little known fact about Element piston is that they are near indestructible:
YouTube - Element piston strenght test Basically your gear's teeth will probably strip before the piston if they're crap.
They make great motors as well. I can vouch for the high speed one since I use it in my p90 with a 11.1v lipo, I can confirm that my P90 gets close to 40 RPS.
http://www.airsoftretreat.com/forums...?topic=89862.0