RE: Hitec 5625 -- 5645
Spend the extra money and get the 5925/5945 servos from Hitec. These are coreless digitals, rugged and well built, and the price can't be beat. You may want to go with the 5975 with the new gears but I don't think it's got enough torque for rudder. Should be fine for ailerons and elevator (if you use one on each half).
I've got a couple of the 5625's and they're fine for sport but I won't put 'em on my big planes.