Question about WOT for yamaha 150

Operating an over-propped motor overloads engine, hence loss of life.
 
If you have a trim indicator on your dash, it indicates motor tilt. I usually have mine @3.5 (approx) for both motors and them trim the boat with the trim tabs. I don't have tab indicators so I use the boat's performance to guide me.
 
I have a 190 Tournament with a 150 Yamaha on it... Its propped 13-3/4x19 and I am only getting 4600 out of it?? Lost on where I should go to...