My first SIG Sumpthin Extra flew fine with an APC 11x6. My new Sumpthin Extra has an OS55AX with a 12x7 APC. I do like the 55AX much better. The engine is much smoother and has a lot more power. They also fit on the same mount and the distances from the mount holes and the rear of the engine to the front are identical, so if an OS46AX will fit, so will the 55. In fact you could easily swap those engines and decide for yourself. Do check your balance when doing this as the .55 may be heavier, but not much.