[Phantom]

To compare some numbers of 87 93 pump gas and e85 (sorry I do not have e10 in my book I got this from)

87
Lower heating value 42.7 kJ/kg
Density 0.740 kg/l
Stoich 14.8

93
Lower heating value 43.5 kJ/kg
Density 0.755 kg/l
Stoich 14.7

E85 Octane 104.2
Lower heating value 26.8 kJ/kg
Density 0.790 kg/l
Stoich 9

So e85 has less energy weighs more and takes more fuel to be at the stoichiomertic ratio.

On a side note Methane Propane or LPG would be a better solution all have a higher energy content an octane rating from 104.5-120 and stoich ratio from 15.5 to 17.2 also they are less dense than Gasoline.

Just to note that on all the above fuels a narrow band O2 should still be able to read fine at lambda=1 (or = to stoich). Also I want to state that many (if not all) flex-fuel cars have a sensor that determines the Ethanol content of the fuel and them uses that info to adjust the ignition timing and possibly fuel injection timing to optimize for the slower burning fuel.