I have a '95 3.0L OMC cobra in a 17.5 ft fiberglass boat and new to boating. Manual calls for 14.5x19 prop as standard, came used with 15x17 prop on. Manual WOT calls for 4,200-4,600 rpm, with the 15x17 I can get to maybe 4,000-4,200. Barely gets 1 average skier (2 skis) out of the water (with 2...