I can tell you it's all in how you drive it, where you drive it and how heavy thumbed you are. My 650 easily used to get 200-225 miles to a tankful, I upgraded to a big bore 850 kit, mild cam upgrade, maverick heads, throttle body, pipe etc, and even with a **** secondary helix allowing a lot of belt slip and excessive rpm at prime cruising speeds I am still getting over 150 a tank. New helix is enroute so, we will see how much better it gets lol.
One ride that shocked me was we had a 100 miles of trail riding thru gnarly terrain one night, I was in low range for most of it, until it was time to head home, I switched to high after we hit the easy trails/dirt roads to head home and just dropped to 3/8s of a tank on pulling into the driveway. I was stunned, seemed like low range allowed for typical better mileage in rough stuff (like 25mph and under trails) than high range did, because the throttle inputs were so small.