I have a 46AX on my Big Stik 40 and mine wouldn't turn a 12x6 APC, not enough rpms. It runs great with an 11x6, and I have it currently setup with a 12x4 which I really like. I ordered a 12x5 to try next. It's a nice running engine. I had a faulty needle valve from the factory that gave me fits (air leak at the o-ring due to poor machining. Let me know how your prop testing turns out, I'm interested in seeing your results. DG