Aren't all 2013 Flexfuel capable? A higher octane gas will help as those engines need to scale to be able to burn E85 properly.
On a side note, I just filled up with Shell 91 V-Power (no ethanol) and I'll see how I do with some mixed driving. Approx -5c outside.
2012 SGM Ti DCT Stock and loving it
OEM multispoke 17" with stock rubber summer-X-ice 3's on stuck rims = awesomesauce