If the Big Stik requires standard servos then you can use a 4.8v or 6v battery with about 1200Mah. Ive never heard the rule to use 6v with 2.4 but with 6v you get higher torque and faster speeds. I like to use 6v in my performance and 3D planes since they have larger control surfaces I want the extra torque to prevent flutter. Also I want the extra speed for 3D. I have seen people fly their Stiks balls to the wall full throttle, so you may benefit by using a 6v battery if you plan on flying like this. I cant comment on the question if 6v negatively affects servos, so far I havent had any problems and I really dont worry about it too much since standard servos are inexpensive and can be replaced without breaking the bank.