Capt. Jim,

RPM on the ground, at zero airspeed, only tells a small part of the story. In fact, it tells a misleading story. We often hear people talk about props for thrust vs. props for speed. This is not really a correct view. The tradeoff is between thrust at low ( or zero ) speed and thrust at high speed. Generally, lower pitched props give higher thrust at low airspeed, and higher pitched props give higher thrust at higher airspeed. Because the engine only has so much power, you can't increase pitch without reducing diameter. Unfortunately, lower diameter props are less efficient, so there is another tradeoff. Ideally, what you want is a prop with enough pitch to give you high speed, large enough diameter to be fairly efficient, and which your engine can spin at close to its peak power. This is complicated, which is why it is a trial and error process. I would suggest trying something a bit higher pitch, with smaller diameter to let it turn faster. A tachometer reading on the ground can give you some idea whether the diameter is small enough to let your high-pitch prop spin fast, but it is misleading, because a high-pitch prop will 'unload' at high airspeed more than an low-pitch prop will.

Good luck,

banktoturn