RE: I got the wrong Prop?
To more accurately figure the prop loading, cube the diameter and multiply by the pitch. The results can be compared favorably.
EXAMPLE:
9x7 prop: 9x9x9x7=5103
10x6 prop: 10x10x10x6=6000
11x5 prop: 11x11x11x5=6655
11x4 prop: 11x11x11x4=5324
If you stay in the same ballpark for total volume, the engine rpms will be very close. The more you depart, the greater or lesser the load on the engine.