I looked into E85 last year. The up side to it is that it's a higher octane I believer around 102-103. So it’s kind of like running a mix of race gas. The down side is that burns less efficient so you go through more of, I believe it burns almost twice as much fuel; if not twice as much close to it. The other downside is that if you have it tuned on E85, and you fill up with regular (even 93-94 octane) your car will run like carp because it’s running hella rich on the regular gas. It could potentially do damage as well especially on boosted applications where you may use the higher octane to run more boost. No higher octane, the extra boost could cause a lot of detonating.
For my car it wasn’t the right path to go. Having a DD that runs on E85 was bad because E85 isn’t available at most places, and I didn’t want to have to worry about my tune if I wasn’t around a gas station that sold it, especially on hot summer days, with higher boost and intake temps. I’d have to remember to pull a shit load of timing when I filled up then the car would just run like ass and what’s the point.