You're in the right rpm range, so no help there. Here are my results: Just me on board....'06 Lowe 24' twin 25" tubes pontoon, double bimini.
'05 Mercury 60 hp, 4cyl., 4 stroke, efi, big foot (ct)....20 mph ( cool day, cold water)
My new mercury 115hp, CT.......26 mph, but, that's at 55-5600...