The ethanol mileage of 245 miles per tank to 265 miles per tank is based on 7 years in the first car and 2 years in the second car with a fill up every 5 to 7 days. So a very large sample size. Driving conditions very similar.
The gasoline tests were in the spring and summer. My test on my new car will be this summer when I drive to one of the pure gasoline stations.
The gasoline fillups each slightly over 300 miles per tank. 30?, 302, 300, and 305.
The first was not technically known to be pure gasoline. It just got my attention. Why the heck did my mileage suddenly increase so dramatically (I got something like 275 on the tank after and then back to 245-265 after that).
Listen, I'm not running a double blind scientific test. But the differences in mileage per tank were not minor. Between 35 and 55 extra miles per tank under similar (mixed usage) driving conditions.
I can usually explain the 245 mileage because I had some "safe your life" jack rabbit entrances onto freeways.
I could get 275 when I drove ideal freeway conditions on long trips (no stops or starts). So about 1.8 mpg higher freeway (but the element has the aerodynamics of a brick so that's understandable).
Why not try it yourself? Every state has a few pure gasoline stations where you can reliably get gasoline. And you can fill up some extra 5 gallon cans and test it yourself under normal driving conditions.