Pro Crappie Prop Size

['03 PC 175]

I just bought a 2003 ProCrappie 175 with a 50hp 2 stroke tracker/mercury motor. I has a 13" aluminum prop on it. My tack reads 6000+ rpm and from everything I've seen that is way to fast. Am I correct that 5000-5500 rpm is what I need to be running? What size prop do I need to get?