The best tool for finding the best prop for your aplication is experimentation. Try different props untill you find one that meets the needs of YOUR flying style. Sometimes the most thrust is not what you are going to want. And what you want your plane to fly like may not be what the next guy wants the same plane to fly like. In general smaller prop diameters with increased pitch will fly faster and larger diameter with reduced pitch will give you more pulling power w/ a lower top speed. Also the larger diameter props create a larger thrust cone enveloping a greater amount of your main wing thus making your ailerons as well as other control surfaces more effective at slower speeds, such as thrust vectored manouvers performed in 3D flying. Small control surfaces that are common on most basic sport models will benifit less from this than the 3D planes with "over sized" control surfaces. Another important thing to know is that the RPM you see on the ground is not even close to the RPM you will reach while flying. The reading you get on the ground is refered to as "static" rpm as the aircraft is restrained and pulling air from in front of it. When the aircraft is flying it allows the prop to "unload" and actually spin at a higher RPM.