You want your engine to stay in a certain RPM range regardless of the prop configuration to keep it in it's power band. Stroke, porting etc. are a certain way inside the engine for a reason based on typical application. So you want to prop to a certain RPM range.

Now, the debate over the efficiency of multi blade props on RC sized engines rages on. I prefer 2 blade props. Electric motors I am sure act different than engines. The biggest problem with multi blades is finding the exact prop as there are so few choices. Not much to experiment with.