Hartzell claims max prop efficiency for my prop is around 2500 but what would they know.
Prop efficiency maybe but engine efficiency variation is a
lot bigger than prop efficiency variation.
I can take you up in my TB20. We climb to FL100, WOT, just into LOP, and play with the prop rpm (2200-2575) while watching the MPG readout on the GPS. It is an impressive confirmation of Cirrus Marketing
But hey as they say (or
used to say) in the USA: fuel is the cheapest thing you can put in your engine