E85 will allow you to make more power than 93 on an affordable fuel so the car can be daily driven with more power at your disposal. If you want to use regular gasoline, you can always make 2 maps for the car on the AEM. One map for 93 with lower boost and less timing for the street, and another for race fuel with advanced timing and more boost for the track.
Wikipedia:
Comparisons to regular gasoline
Depending on composition and source, E85 has an octane rating of 100 - 105[4] compared to regular gasoline’s typical rating of 85 - 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. Since the reciprocating mass of the engine increases in proportion to the displacement of the engine E85 has a higher potential efficiency for an engine of equal power.
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[5], 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 5-10% less expensive in most areas.[6] More than 20 fueling stations across the Midwest are selling E85 at the same price as gasoline.[7] 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.[8][9] 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.[10]