Seth, I think around the 150-175 hp range you start getting close to 50. Of course all depends on what it is on, weight factor etc. The bigger you go after that the torque starts making a difference for carrying more weight, bigger boats, etc.
With my boat I hit 45.8 gps with 3 adults, 2 kids, all of our fishing gear and live well full across Clearwater in heavy chop. That is only 4mph slower than my top speed so far with the boat empty but that was still during break-in with a WOT run for about 30 seconds.
Once you hit 50 it gets harder to get more out of it, you can only spin the pump so fast.
You need to break down and get that 1860 you been wanting with a 225 or 250. :lol: