Just did 370 miles today ( mixed 140 highway miles, the rest back roads ) and averaged 45 MPG ( per the computer ). 800xc with stock exhaust and tires. Did about 80 MPH down the highway with the panniers off. My reserve light comes on around 180 miles or so and it always takes 3.8 gallons at the pump. I'm guessing I could do 220-240 miles on a tank before I'm walking.
The Tiger's range isn't what I was expecting but it is an amazing bike. Its too fun and functional to complain about the range. For those looking for ultra range, get a Rotopax, strap it to the back, the front, side or anywhere it fits and go. Tank size shouldn't limit anyone's possibilities.