Power wise: Specific heat for C8H18 is around 42.6 MJ/kg and E85 is around 32.7 MJ/kg, which is 30% more for regular gas
Mileage: Per 60L tank, C8H18 is around 1907 MJ and E85 is around 1536 MJ, which is 24% more for regular gas
CO2 emission: C8H18 is around 12.5% or 72g/MJ and E85 is around 12.3% or 69 g/MJ, which again, C8H18 is a bit higher
MJ = megajoule = 1*10^6 joules, where a joule is a derived unit of work or energy.
read :
http://en.wikipedia.org/wiki/E-85
interesting note, "Minnesota has the largest number of E85 fuel pumps of any U.S. state, with 158 of the 580+ pumps in the country"