I've been tuning with E85 for about 6+ years now and i have tuned MANY engines on it from 1000+HP 4 cylinder to V8s to the 3.8 buick engine. Being a tuner for a shop and tuning for almost 2 decades now i have noticed the same to better performance with E85 then C16 which is 15$ a gallon. E85 doesn't kill your o2 sensors either which is a plus. If you have easy access to it i say go for it!! Its a no brainer.
Few tips if you do run E85:
Just check the tips of your injectors from time to time to make sure your not getting any build up on the tips. If so its a quick easy fix of soaking them in regular ol 87 octane pump gas OR running a tank of pump gas through the engine and they will clean right up, which is what i do. This also cleans any gunk you can get in your intake ports of your intake and cylinder head as well and something id recommend 1-2 times a year. Some get the build up others don't.... Honestly cant answer that one as to why with 100% certainty but even so the price per HP is WELL worth it! And it never hurts to check ethanol content as some places depending on area will lower ethanol content for winter for better cold starts. But even at a minimum of 68-70% ethanol u can still make the power C16 does for a fraction of the cost. I checked my local station just the other day and it was still 79% and we should be in full winter ethanol content by now. I'm in southern Indiana and our E85 stays very close year round here at the Thortons gas stations that sell it around here. Another thing is to not let E85 set in your injectors for months without starting your engine and letting the injectors work as alcohol attracts moister and can rust the insides of injectors if let set long enough. A few weeks is no issue but months on end i wouldn't recommend... Especially if you are in a humid climate where moister is higher.