I have used both motors on that plane, 55AX is really the way to go. The 46AX will do the job, but if you are learning 3D the 55AX will get you out of hairier situations. With the 55AX you can run the APC 13x4 with no problem, throttle response will be good and pull out power will be good also. But I think one of the biggest advantages with the 13x4 is that, you have a larger area of airflow since you have a larger diameter prop. The more air hitting those flight controls the better. Ive got a Saito 82 on the OMP pro yak with a 14 diameter prop and it feels alot more responsive to my inputs because Ive got so much air hitting the surfaces.