Great question, I've been debating this myself. I've got a Brison 3.2 in a Lanier CAP. I've tried a 20x10, a 21x10 and a 22x8. I kinda like the 22" prop for landing approaches----it slows the plane down nicely (bigger prop arc acts better as a brake??). My 22" prop is a relatively inexpensive wood prop----and its very noisy. The 21x10 is a carbon fiber prop----the plane is much quieter and seems to be more efficient (lower rpms and lower throttle settings). Problem is that both 10 pitch props give the plane more speed, even at lower throttle settings. Plane is much harder to slow down on landing approaches. Seems like I can't find the optimal balance between these props. If any of you have got any ideas,.....WarpedWing.