I ve got a question on various prop calculators on the net.I have 5000 rpm a 32in bravo1 4 blade and running 81 maybe 82mph.The calculators on the net say that is over 20 % slip.The guys at merc racing tell me its 15 and acceptable ? any comments ? the boat is a 30 deepv with small steps.2001 30y2k superboat.