Here is a link to a calculator. It will tell you how many oz of torque you need.

http://www.csd.net/~cgadd/eflight/calcs_servo.htm

If you want small, powerful servos, check out BlueBird servos (up to 57 oz @4.8 volts).
http://www.bphobbies.com

I use the Bluebird servos all the time. The only negative is you want the metal gear servos. The nylon gears don't hold up, especially if pushed.