Go for more diameter before more pitch. My math indicates prop lift (thrust) varies with:

- diameter to the third power
- engine speed (rpm) to the second power
- pitch to the first power

Also, it will vary directly (to the first power) with air density i.e. your ASL.

The link below is to a thread that gives some formulas where static thrust varies with the fourth power of diameter. I think those came from a magazine:

http://www.rcuniverse.com/showthread...light=formulas

(In the absence of further thought, I don't know who is wrong.... one of us is?!?!?)

In any event, and as already been stated, for any given rpm, you'll win more thrust by increasing the diameter even if it means decreasing pitch.

The ThrustHP program gives a thrust estimate the does not vary at all with pitch. I couldn't find any info about what how thrust HP comes up with these numbers. I don't see how it could be correct..