My 02 KDX 200 with a stock tank gets +/- 80 miles per tank in tight "on and off the gas" hilly terrain. It will get 140 miles per tank in relatively open "dual sport" riding and yes I have about 6 witnesses who made the rides with me and saw me fill up during gas stops.
This milage was consistent from central Mississippi to SE Kentucky, and NW Arkansas (Ozarks). In the Ozark 200 Dual Sport, our first gas stop was at 49 miles. I used 1.3 gallons (2.9 gallon tank) and a guy from Iowa on a KDX 220 used 1.5 gallons. There was a lot of mountain climbing in that first 49 miles. Not bad, especially considering my CR250 (I sold to get my KDX) got a whopping 22 miles per tank.
The key is proper jetting and gearing. KDX's are terribly weak and rich from the factory.
JCW