Bmetro, the best way to really analyze and compare propping is by comparing the Max RPM range of the engine and compare that to the actual RPM"s when at Wide open Throttle (WOT). Don't necessarily look at speed as that can be influenced by sea state, tides and current. The RPM at WOT should be somewhere within the range of the MAx. RPm for the engine. Proper drive trim attitude and trim tab will also have some impact on this.
Going up in pitch will decrease hole shot, but increase cruising speed at a given RPM. Going down in pitch will increase hole shot but decrease cruising speed at a given RPM. If top end is what you're looking for, increase pitch. If hole shot is what you're lookng for, decrease. This is provided that you remain within the Max. RPM range of the engine.
I believe the Max. RPM range for the 6.2L MPI is 4800 - 5200.
As for mixing prop pitches, I'd take a look at the Mercruiser prop calculator as well.