Fountain97

I have a 27 foot fountain with a 500 hp carb running a 24 hydromotive 4 blade. I have heard several different stories about the top speed mine is running 73 at 5100rpm on gps am I missing something here everyone else claims to be closer to 80? I also noticed several people have the 415hp motor running a 26 pitch prop how can this be is my motor getting worn out it has 527 hours on it and runs great. It currently is using some oil I am told this is normal but I am not buying into that maybe how much is normal.