A buddy of mine re-opened the old Y&O prop line some years back. As part of this he wanted to know why some props work and some are only good for stirring coffee. He found that much like Dick mentions in an early reply that most props are numbered because they are a little flatter than the big one but coarser than the flat one and I happen to be holding this number stamp so I think I'll use it.... OK, it's not THAT bad but from testing a lot of props he did find that the numbers stamped or molded in typically only describe the prop for a rather small portion of the blade. APC's were better than most on this account with most of the rapid reduction in true pitch only occuring in the first 1/4 out from the hub and a little reduction in pitch as washout in the last part of the tips.

Other than that all I see here is folks pretty much agreeing that it's the match to the engine and that electrics have changed the face of the issue pretty much completely.