I have a 3-blade whirlwind ground adjustable prop on my ULPower 350iS/701 Sky Jeep.

I started with a fairly steep prop pitch and have been gradually backing it off with less pitch. It “feels right” at this prop pitch setting and will climbout pretty steeply at ~2,900rpm WOT.

I got these specs today with straight and stable flight at 40 deg OAT:
55mph@1930rpm, 3.0gph
65mph@2060rpm, 3.5gph
75mph@2250rpm, 4.2gph
85mph@2500rpm, 5.2gph

Unfortunately, I didn't record the specs at the higher pitch settings, but think I may be beginning to loose fuel efficiency as I lower the pitch and increase the rpm.

Since it is a very “draggy” airplane, I am afraid I could loose some of this excellent fuel economy by adjusting for even less prop pitch. This efficiency is pretty amazing and it already goes up like a rocket, so should I stop here or keep adjusting?

What have you all found as your happy-medium for 'power (rpm) vs. efficiency'?

Thanks!