RE: what rpm to operate at?
I agree with Silversurfer. I played with a lot of props from 10x6 to 12x6 an even a couple of 3 blades with my OS .46 SF. An 11X7 had enough speed and enough "dig" with my Sig Kougar (6lb) to get good uplines and managable downlines. It turns about 10-11k on the ground.