104 should be plenty with 12.5, but as Tech said it is dependent on many other factors especially squish and piston top/combustion chamber configuration. I've run 14:1 on 104 with coated piston tops and "massaged" chambers.

As far as E-85, we have a distinct advantage here because we are 7 miles from an ethanol plant and are assured of a supply and good quality minus all the shipping and storage contamination issues. Absolutely nothing worse then e-85 being sold out of an old tank that was previously used for gasoline. The ethanol will work all the contamination, rust, crap, water, and crud out of that old storage tank and guess where it ends up. E-85 works great for us, just be sure of your supply!!!