My target RPM at WOT under normal load/conditions would be 4,900 - 5K. Only in perfect conditions (light gear/people/fuel load, cool/dry air, light chop) would you want to be able to tickle the rev limiter. That combo will never see 70 MPH GPS. Have the speeds you've been listing been GPS speeds? I would try a 23" Mirage Plus. The three blade will be your fastest prop and the Plus has cup that the standard Mirage doesn't. Your boat will like the cup on the 3 blade.

Does the boat have indicators? Are you trimming the drive up at WOT? My Fountain with a 496HO will only get to about 4800-4900 with the trim at 4 on the indicator. Moving it to 5 gains another 150-200rpm and another few mph.