Ok, the actual octane rating of e85 (assuming it is actual 85% ethanol) is only about 96 AKI (its 105 octane in the RON scale).... which is the scale that the US and Canada use for their octane rating (RONxMON/2)...
the reason it seems like a higher octane is because it burns a lot cooler than regular gasoline..
In regards to the mpg (or mpd in this case) you have to consider your driving habits more than anything. first off, with e85, you should really be tuning in open loop if you can. This will save you some highway (and city for that matter) mpgs. I get about 23-24 (91 premium was 28-29) mpg on the highway running 50* of timing with an average afr (gas afr that is) of ~16/1. Around town I get just under 20mpgs (91 premium was ~21) with about a 15.5/1 afr. So as long as your % mpg loss isn more than the % difference in the price of premium youre still going to be saving money but each person will have different results pending.
But in the end you dont get e85 for the economical factor anyway... and if you do most of your driving around town youre not gonna lose that much mpg anyway... just the biggest hits on the highway...
