Since ive got a 38 gallon tank in my tundra I figured id get a tankfull of e-15 and see what type of milage i get. So far it's hard to tell a difference between the e-10 that most gas stations sell.
I use e10 in all my vehicles - even the motorcycle. I lost about 2 - 3 mpg compared to conventional gas. Very few places even sell the higher e15+ in my area.