1996 Mariner 50 H.P. propeller help

I have a 1996 Mariner (2- Stroke) 50 H.P. and would like to get more top end speed. I resides on an aluminum 1998 160SC MonArk (hull weight of around 900 lbs. empty). By myself with a 13.5" pitch prop I can achieve 32 to 33 MPH. I do not have a tachometer on the boat but I trim it up until it starts to rev up then back it down a little. I understand that a higher pitch will give me more top end while sacrificing the hole shot. It will also lower my top end RPM. I fish and will never need to pull skiers. Just wonder if I can save $ and time by tapping the others that have gone through this. How much more MPH could I get if I jump to say a 15" or 16" prop? Where is the point of diminishing returns. Thanks for all the help.

Boat speed likely will not change much.-----RPM of motor will change for sure.----I doubt you can spin a 16" prop.