I commute about 80 miles round trip on the Multi GT. It's a pretty good upgrade most the way to work, but conversely downhill on the way back.
I usually cruise 80-85 on the speedo, realizing it's off by about 5 mph. I too average between 40-43 religiously.
I filled up a couple days ago and figured I'd try an experiment. My goal was to keep the speed between 70-79 and see what would happen to my mpg. After 2 round trips to work, 160 miles, and keeping the speed mostly under 80, but above 72, my mpg registered at 45.
I imagine if I actually went the speed limit, my mileage would easily be in the 50+ range. But the fun factor would nonexistent. Then again, I didn't buy this bike to be bored...
Dave In Valencia
You are dead a long time, so enjoy the time you have while you are alive