I'm running a O.S. 91FX with a 15x4 prop. Has great power to weight. Accelerates Straight up and hovers on about 2/3 throttle.

I've tried a a 14x6 prop to start but noticed some prop "stalling" at hover. Sounded like it was buzzing. Went to a 16x4, but seemed to throttle up a little slow. 15x4 has nearlyt instant response and uses less throttle to hover than the 14x6.