With larger torque ratings, come larger stronger gear trains and motors. Don't rely on the 6V torque ratings of servos. That number is 'bonus torque', I would say, for an already strong servo. I like to use the Hitec 645MG. It has well over 100 oz of torque (at 4.8), metal gears, and can be found all day for under $30. Great for the rudder on a tail dragger, among other things. Beyond that, although I use JR, hear are my thoughts on larger planes.

Throttle-if gas, 5-pole or digital standard servo
Choke-same
Ailerons- (2 servos)-120 oz each or better, (4 servos)-60 oz each or better
Rudder- 100oz metal gear or better
Elevators- (split) 80oz metal gear or better

The tail can take a beating on tail draggers hence the metal gears.