Going from using 1 gallon of petro for 15 miles, to using (assume 30 mpg E85 so math is easier) .075 of a gallon of petro for the same 15 miles, winter blend of E70 would use 0.15 gallons of petrol.
Check out the Buick Regal Turbo, one claim of 5-8% MPG drop using E85. I saw somewhere a claim of equal MPG on it yesterday, never heard of it till yesterday. Too pricey for me, but I think the techonology will work down to the Cruze. (EPA rating are the nomal 1/3 third off).
2011 Buick Regal Turbo features flex-fuel capability