I flip flop all the time and I havent noticed a difference. My closest station with E85 is about 20 miles away so I only fill up when I am up around that area on the weekends. I havent seen any negative effects running wise, but I tend to get 12mpg with the E85 compared to the 14mpg with regular.

 

I found some, but they wanted $3.83 a gallon for it. I tried it anyway. It's 105 octane. Maybe I should load my 91 octane performance tune, now