With my '84 20V Fisherman my 150 Yamaha runs WOT at 5600rpm (light load) is running 42 mph...getting about 3 GPH at 3800 rpm (25 mph)- Stiletto 14x17 cupped three blade.
With a 14x17 (no cup) I get WOT at 5400 rpm (heavy load) is running 45 mph... getting about 1.75 mpg at 3800 rpm (28 mph.)

I've been experimenting lately trying to move the most weight with the best fuel economy.