In my experience, the use of 10% ethanol fuel reduces my MPG by about 10%. I know the "experts" say it should only be reduced 2-3%, but in 4 different vehicles, INCLUDING my 8.1L W-22 Motorhome, the measured reduction in MPG over time hovers right around 10%. Pretty much all we have here in the NorthEast and I believe most of the East Coast, is 10% ethanol blends. It's darn near impossible to find pure gas. But when I'm on the road and DO find it, I use it!
So, IF you can find REAL gas for under a 10% price premium, I'd say go for it!
~Rick