At home, in south Texas, I generally get in the low 70s for mpg. There are no gas stations near us that have non-ethanol gas. Sea level. Generally riding at 30 mph or 55 mph. Short trips.
Here in the Black Hills we are able to find non-ethanol premium gas (passed by two stations today that only had ethanol in all grades). Elevations vary between 3,500 and 5,000'. Very little stop and go riding, but we are enthusiastically cruising through curves and hills. My mileage with the 250 GTS has been in the low 80s here. Yeah, 10 mpg better, on average.
Today, I hit an all-time high mpg: 92 mpg! Yeah, that seems incredible to me, too. I do understand that a click or two on the fuel pump handle can make a difference with these small amounts. I have gotten pretty good at getting the tank full without (too much) overflow.
Elevation? Non-ethanol? The scoot likes being pushed through the curves? Low humidity? Tailwinds that change with the curves to stay with us? The scoot is as happy to be cruising as I am??

For some perspective, my wife is getting better than average her on her PCX (153cc): 120 mpg.
Yeah, I'm just calling it a sweet spot.
Anyone else want to share what they generally get for MPG on their 250 or 300 GTS?