If you can calculate the MPG difference between Summer and Winter formulation gasoline, you might be able to tell the difference.
For me, the noticeable difference was in my truck, which would sit for 2-3 weeks at a time, and would run AWFUL if it ran at all on E10, for several minutes, until it got through the water/alkie mix that had separated to the bottom of the tank. Once I switched to E-free, those starting and warmup problems went away (with no engine associated repairs).
Lately, however, I've fixed the long laundry list of issues with that truck (it's a Dodge) and run the truck at least weekly, so phase separation is not the issue it used to be. I rarely put E-Free in it any more. Just a half tank-full when I make the last Outdoor Power Equipment E-Free gas run of the Fall, to help it get through the Winter when I use it a bit less, and water in gas issues are more prominent.