I tried props ranging from a 11x9 (yes my LHS had one) to a 14x4 (from my 75ax) on this engine. My observation is that a 11x9 is too speedy and a 14x4 too large. I would suggest 11x8 / 12x8 for sports and 13x4 for 3D. I currently have a 13x6 on my Reactor but that is just becuase I want to have a absolutely balanced prop and the MAS 13X6 S2 I have is just that

Ameyam