I have a friend that just got a 23' Larson BR boat. When he runs it at WOT the rpm goes 5400 to 5500 rpm with his 2 kids , wife and him with a full tank of fuel. The motor is a 5.0 merc 280hp.It has a 3 blade 19 pitch aluminum on it now. What prop/size should it have on it? or where should the rpm be for that motor? is 5400 or 5500 rpm right for that motor?