Worst I ever got was 55 miles to reserve, or maybe 70 to dry tank, WOT on pavement into headwind. Best I ever got was 105 to reserve, putting along backcountry lanes at 26-35 mph, or maybe 135 to dry tank. Average is around 75-80 miles to reserve, 115 to dry tank. Tire pressure is important! Running 20 psi will get the best mileage at higher speeds at the expense of comfort. I usually run 16/18 on pavement and 14/15 in the dirt....That best number was probably with 16/18.
I often carry a 32 oz. MSR bottle just in case.