LOW RPM's

I have a 1989 yamaha 90 hp. Its on a 15ft invader with a deep V.
I can get 37mph by myself fully trimmed. The tach will go to 4800rpm's. With four people I get 35 mph and 4600rpm's. The prop is a michigan vortex 13 x 17. The engine runs great. Should I go do to a 13 x 15 to get the extra rpm's? What would be the benifits?

[boats.net]

I like to prop them up close to 5500 rpm's, you might try a smaller pitch prop.