Originally Posted by Mothra

One thing to remember is your basic calculus. Power is torque integrated with respect to time. Which goes back to the gearing and RPM ideas. If you keep torque constant, but spin it twice as fast, you'll get twice the power. That's why the fastest sprinters spin such high-RPMs; there's a physiological limit to how much force & torque the human body can exert on the cranks. But if you spin it faster, you'll get more power & speed. Here's some auto sites that discuss torque & HP:
http://www.v8914.com/Horsepower-v-torque.htm
http://www.epi-eng.com/BAS-PwrTrq.htm
http://www.team-integra.net/sections...?ArticleID=467
http://www.howstuffworks.com/question381.htm

It's not so much the torque, but the linear force in shear at the teeth that'll break them off. Calculate cross-sectional area of teeth at the contact point and figure breaking force at yield-strength. Divide by number of teeth and divide torque through radius of gears and see which is greater. Power is just how fast you spin the gear, so it won't hurt them that much to spin it faster... until you get into 200,000rpms+ where inertial forces starts coming into play.