47.5 mph, according to my GPS, at 6,000 RPM, which is the max for my engine. That's using a 14.5 x 18 SS prop.

I have another 14 x 20 prop that came with the boat, which I estimate would crank it to above 50 mph. I've never bothered to check it, though, because the other prop works so well for everything throughout the entire power range, and I think it's good to prop an engine so that it runs toward the high end of its RPM range. I rarely need max top-end speed, anyway.