I have many customers with the gm factory flex fuel LHU 2.0 di engine and running full E85 (70+% indicated) will definitely result in a ~20% or more increase in fuel consumption. You can take advantage of the higher knock resistance and increased charge cooling to safely run much higher power (compared to 93 octane gas) but even when optimized for a given compression ratio E85 will not result in greater thermal efficiency (just a small bump in VE from the charge cooling derived mainly from the heat of vaporization X the increased volume of ethanol fuel injected ).
The lower energy density of the E85 fuel always requires increased fuel consumption. but I love the stuff and will gladly take the hit in fuel economy for the improved performance. My 2011 cruze also eats a steady diet of E85, methanol, water, peroxide, nitrous oxide and nitromethane ;)
