ORIGINAL: Geistware
Basically a plane being restrained will have a lower RPM compared to one that has unloaded in the air which will have a higher Rpm. I would consider that unless you are hovering, you will get higher RPM's and speed in the air.
there you go. I put the caveats in, and they went right over your head...put a governor on the engines, so they will only turn 10000 rpm
I will bet you that a 12x6 turning 10000rpm will pull a given (that means the exact same airplane) airplane at a higher speed than a 10x6 turning 10000 rpm. They will both get that given (same) airplane up to any spped you chose faster than a 10x4 turning the same rpm (10000)
the pitch helps you decide, and does have some significance. Bernouli gets a say-so in the equation, however...
ask a heli guy who uses a governor what happens to his pitch curves when he changes the disk diameter...