I would leave the prop alone for right now and drill out the exhaust. It will be the best bang for the buck and you will not lose any reliability. Adding a larger carb without drilling out the exhaust does not make sense to me. You are just flooding the engine with more fuel without opening up the exhaust to let the fuel out and to let the motor breath. Drill the exhaust first, my guess is you pick up a few hundred rpm with the same prop. Good Luck