Sadly, I only have experience with one bike. I bought a "old" bike two weeks back, '87 Intruder VS700. It's a VTwin that's 700CC but runs closer to a 750. I've only got two tanks in it, and I've not been at ALL gentle with it, but the average right now is about 48 MPG. Cruising on the secondary roads between 55-60 MPH and hitting short stints up to... well, fast
. I'll be making longer trips starting in June with it but I expect those to be about 50 MPG average tanks (100 miles round trip into work). I'm pretty happy with that result, really.