You'll lose quite a bit of power, on top of the poor mileage. My truck is set up for E85, but I'll never put that crap in my tank.
The stations around this state rip us off diluting the regular fuel enough as it is - I've read alcohol levels on my scan tool well OVER 20% in regular gasoline, when it's posted at the pump to be no more than 10%! This is outright THEFT, and yet you don't hear a peep about it. Most people in this state wouldn't know what a spare tire looks like, let alone how to operate a scan tool. Sad reality of this part of the country. Most probably wouldn't even care if they knew the truth.
The reason I checked that day was because my mileage sucked, and the truck clearly lost a substantial amount of torque. I was expecting some pending codes for some type of sensor failure. No wonder ... and that was only at 23% or so!
This is the main reason I have a job! I clean carburetors, flush tanks, and replace fuel lines all day long on motorcycles, weedwackers, chainsaws, lawn tractors, & push mowers. The stuff is constantly causing problems for people. It's got so bad that lots of equipment has gone back to adjustable carburetors (they hide the screws sometimes though), to keep them from burning up.
What's our government doing about this? Pushing for E15 ....