Interesting question Sseisup. I hadn't heard of e85 and have yet to see it sold here in CT but almost every pump has a sticker saying "contains 10% ethanol" but found this; E85 - Wikipedia, the free encyclopedia
This article is critical an I dunno. States you will loose some umph and pay almost as much with no advantage. The Honda GX50 manual advises against more then 10% ethanol. I still hate OPEC!!! lol
From that page;
"E85 has an octane rating higher than that of regular gasoline's typical rating of 87, or premium gasoline's 91-93. This allows it to be used in higher compression engines which tend to produce more power per unit of displacement than their gasoline counterparts. The Renewable Fuels Foundation states in its Changes in Gasloine IV manual, "There is no requirement to post octane on an E85 dispenser. If a retailer chooses to post octane, they should be aware that the often cited 105 octane is incorrect. This number was derived by using ethanolís blending octane value in gasoline. This is not the proper way to calculate the octane of E85. Ethanolís true octane value should be used to calculate E85ís octane value. This results in an octane range of 94-96 (R+M)/2. These calculations have been confirmed by actual octane engine tests." 
One complication is that use of gasoline in an engine with a high enough compression ratio to use E85 efficiently would likely result in catastrophic failure due to engine detonation, as the octane rating of gasoline is not high enough to withstand the greater compression ratios in use in an engine specifically designed to run on E85. Use of E85 in an engine designed specifically for gasoline would result in a loss of the potential efficiency that it is possible to gain with this fuel. Using E85 in a gasoline engine has the drawback of achieving lower fuel economy as more fuel is needed per unit air (stoichiometric fuel ratio) to run the engine in comparison with gasoline. This corresponds to a lower heating value (units of energy per unit mass) for E85 than gasoline.
E85 consumes more fuel in flex fuel type vehicles when the vehicle uses the same compression for both E85 and gasoline because of its lower stoichiometric fuel ratio and lower heating value. European car maker Saab currently produces a flex fuel version of their 9-5 sedan which consumes the same amount of fuel whether running e85 or gasoline, though it is not available in the United States. So in order to save money at the pump with current flex fuel vehicles available in the United States the price of E85 must be much lower than gasoline. Currently E85 is about 15% less expensive in most areas. More than 20 fueling stations across the Midwest are selling E85 at the same price as gasoline. E85 also gets less MPG, at least in flex fuel vehicles. In one test, a Chevy Tahoe flex-fuel vehicle averaged 18 MPG [U.S. gallons] for gasoline, and 13 MPG for E85, or 28% fewer MPG than gasoline. In that test, the cost of gas averaged $3.42, while the cost for E85 averaged $3.09, or 90% the cost of gasoline. In another test, however, a fleet of Ford Tauruses averaged only about 6% fewer miles per gallon in the ethanol-based vehicles as compared to traditional, gas-powered Tauruses. (Please note this is questionable as the reference provided is non-existent on NREL's website.)"