Close to 80 mpg on my Diamo which has the OHC motor and a 44 tooth rear sprocket replacing the stock 54 which was ridiculous. It's all in town with very little out on the roads. Just can't bring myself to run it on the highway when I have an old GoldWing that gets 40 and a SV650 which gets high 40s. Something about the proper tool for the job, I guess.
I see the Diamo more as a great around town bike which is most of my riding now days, and as an off road utility bike down on my place since I sold my 4x4 and have nothing else.