I have an 89 17' four winn with a 2.3L OMC about 2050#.
I am running about 5200-5600 RPM at max and getting about 30mph (verified with gps), lite cruising at 4800-5000 rpm and getting about 25mph.
The prop that is on it is alluminum and a 13x19, the specs say I can use up to a 14x(something)...