high torque servos are underrated. they make a huge difference in how an airplane flies and behaves.
40oz servos will work just fine but for the same price (or cheaper) the servos below (very high torque) make a huge difference (like straping a .75 engine into a .40 plane, except in a control surface sorta way)

http://hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=2&Product_Name=HXT_10kg_ Servo_(metal_gear)_55g_/_10kg_/_.16sec
http://hobbycity.com/hobbyking/store..._bearing_servo

at 6.9 kg of torque (that well over 225oz) your control surfaces will stay where you want them too. this makes a huge difference when knife edgeing, 3d in general or just doing simple things like quick rolls.

best thing is they are cheaper than the others yet are just as reliable (ive fried quite a few 40oz servos from tower by just wearing them out....havnt fried one of these yet and i have well over of these 20 servos in active flying models)
they center jsut as well if not better than the 10 dollar tower servos.

dont think high torque servos make a difference? try for yourself and see. its very noticible and wont break the bank