It will be higher octane than pump fuel, how much varies. I've seen it behave like 100 octane and I've also seen it perform much much better. It is very unstable. If it were regulated like pump gas was to require X minimum octane, it might be different.
E85 vs 91 octane, E85 will cost you more at the pump. E85 vs 100 octane, E85 will be cheaper at the pump but more attention required.
IMO fuel is just like any thing else in the auto industry. You can pay a little more and not have to worry about it, or you can pay a lot less but involve a majority of your time.
03 325i - Daily Driver
05 GTO 750 RWHP - For Sale
09 e92 - Pending purchase.