Sorry Forrest it isn't "all about proper weight/Prop match". It is part of it. The faster you go the more friction is added multiplying the amount of torque/HP required. You cant put a 19" prop on a 5hp and get 50 MPH out of it. There is hull design, horse power, friction and torque in the equation.
If you put too large of a prop on a boat it may or will take the RPM's down below its powerband. It will or can make your boat slower. It can also be hard on your internal engine parts by creating more strain on bearing surfaces. Most manufacturers will give you an RPM range to work with a particular engine. Usually it will be within a 500 rpm range. This is where you want your engine to run when it is wide open with a normal load. A top quality stainless prop is the way to gain performance. Aluminum blades will flex a little at high rpm and you lose a little bit.