Hi,
I own a 50 etec on a 4.6m stabicraft. It gets onto the plane easy, wot at 5700rpm does 28.5 knots and uses about 12l of fuel for 2 hours of run time on a day out, with varing rpms, idle to wot. IT doesn't vary much when fully loaded. It also uses stuff all oil, put about an egg cup in after every trip.. Have 65 hours on the motor and used about 3/4 of a gallon bottle of xd100, with the engine oil bottle still full.