Answer more complex. Would need prop size and pitch. Also wind, wave and current.
I usually cruise at around 2250 mostly for fuel consumption. At that engine rpm I use .75 gallons/hr. On a “calm” day, maybe 6.5 knots. As you increase rpms fuel consumption is exponential. But so is power.
I believe I am still using the 12 inch pitch. The 11 inch didn’t have enough power to get me through the island cuts against the current.
Excessive heat at idle is not good. Under load?

Stan,
Unabated is right to ask if “Excessive heat at idle is not good. Under load?”..
I would do this before investigating any propeller issues if you experience engine overheating at idle or low engine speeds..
First.. I would suggest looking at your raw water input strainer (if it is clear you should see water flowing thru there nicely with engine running) or lines to make sure they are not restricted or blocked..
Second… I would check your water pump impeller for wear or broken arms/ribs..
Third.. I would check the input to the heat exchanger to see if it may be clogged with old broken water pump impeller bits..
Hope this helps..
John
Mela