I have a stratos 275 f/s with a evinrude XP 150hp that I just bought . My problem is being under propped right now it has a 14 1/2 18p Racker stainless steel running 6400rpm (no I don't keep it there) at 52mph. What prop size should I be looking to get to get it a realistic RPM range of 5300 to 5500rpm.