Your opionions will be appreciated. I have twin 6bta 330 turbo Cummins, (5.9 liter) in my boat. Boat weight approx 32000lbs. The engines have 750 hrs and are in perfect operating conditon, no issues. For fuel economy I like to run them from 1650 to 1850 RPM and that pushes me along at 9 to 10...