My recent experience fits this discussion.

Previously, I mostly thought about power and props in terms of maximum speed, but started doing some 3D flying last year, learning to hover, etc., I was using a YS .91FX and a prop I had heard recommended many times, a 14 X 8.

After only a few flights, a more experienced 3D flyer suggested a 15 X 6. The results were better 3D flight and better engine performance in those regimes.... interesting.