I finally went all out on prop testing yesterday with my Phoenix Extra w/OS 55ax. It has always flown well, but not vertically and didn't have the power I thought I would have with it. I have tried 13x7, 12x7, 11x8, 11x7, and finally found out that the 12x4 is my new favorite prop! She would tear holes in the sky with the 11x8, but would not accelerate verticaly like I wanted. The 12x4 did it. It still seems to have alot of straight line speed as well. I have the same prop on my decathlon w/46fx and I should've tried it sooner. The decathlon doesn't want to fly on an 11x7, it needs alot of torque.