Brahma, with stock intake, TORs and Triumph TORs tune dropped as low as 26 MPH when the front bearing were seized up and the idle was high. Last week end I got 37MPH coming back from Gettysburg. Best I ever got was riding north out of Denver to Sturgis in 2014, I hit 42 Mph.
I remember like 20 years ago, one of the big time truck makers was crowing about their truck that got a whopping 10 mpg! I reckon it was wheezy on hills too, but ya never hear anyone saying anything about it anymore...so long as you got an APU and don't idle during downtime!
I pull a car trailer which is an aerodynamic mess. I've heard of a few driver claiming 9+mpg, but That's with light loads driving 60 downhill both ways...
After riding mostly in the city lately, I got 33 MPG at the first fill-up this morning. After riding through the mountains today (elevations between 6,000' and 10,000', hot weather, mostly at about 50-60 MPH), I was pleasantly surprised to get 48 MPG when I refilled the tank on the way home tonight. Stock 2014 Roadster.