You should be fine with 4x2721 on the ailerons. I use one 4721 on my Midwest Extra Rudder and it holds up fine. I also have the older H9 Extra with the wing that has one servo per aileron and I have an 8411 in each wing, and they seem to be holding up pretty well. I don't have the throws on the ailerons maxed out, but they are plenty efficient.