The 450 I demo'd got somewhere between 50 and 60mpg, which impressed me mightily.
On the 500, my first and second rides were about 30 miles each, and I figured I would not refill between them to get a better baseline on mileage. This was all technical singletrack, my old carb'd 450 gets about 35 in this use. After 64 miles:
(note the fuel level).
It ran to the truck, but would not restart. Guess I shaved that close!
And just filled it up at a pump:
So I believe the usable capacity of the 500 is 2.2 gallons. I'd heard a variety of figures, thought I'd post my experience as a baseline.
Now, what remains to be seen is why I got 29.5 miles per gallon (I was even being somewhat nice, during break in), when that is so far from what I got on the 450.