Don't try so hard to get simple answers. There are lots of things that narrow the answers, and often narrow the general answer right out of being correct for your particular situation.

Generally, more diameter will let the engine pull better. Unless of course, the engine doesn't have the torque to do it. And you know what..... if the engine does have the power to do it, the rpms probably will still go down. And yet the airplane will fly better.

What works better than having a pocket full of "rules of thumb", when it comes to choosing the best prop for your airplane, is to have a pocket full of props.