Was running the engine a little lower the other day with a 28" ProMax prop, just to see some fuel numbers. Took some pics. Basically around 4 gph to 4.3 gph at 40 to 44 MPH, depending, and around 3200 to 3400 RPM. That's about 10 MPG's at 40 + MPH.
I absolutely love this boat and setup. The problem with an Allison is that it makes everything else feel like a tug boat. If I could setup a new 150 ProXS with a 1.75 sportmaster, it would be perfect.