I've had good luck with ethanol in 2 different car(2.0L and 1.6 L). I saw increases with E15 (give or take since we don't know the % of the source) of about 3%. I have run varying mixtures of ethanol from E0 to E85. A mixture of E50 only decreased my FE by 7%. I took a huge hit at E85 almost 26%. I think that a mixture at E50 with the car tuned to run on it and you might get it down to 5% loss or so.
Here's
a link that I think that article came from. It's from the ethanol folks so take it with a grain of salt but I have had experience along the same line.
GHG are down, (15-25%) depending on how they make it, with ethanol but there are some nasty small particle stuff to
deal with. E85 increased acetaldehyde
(1250%-4340%) and formaldehyde (7%-240%), two important ozone precursors. So pick your poison.