I have made several different road trips lately with my Continental, some tuned for straight 93 and others with additional spark set up for more E.
The best mileage and performance I get is with about a 35% E blend. Frankly, I was surprised. I expected mileage to take a hit with higher levels of E but not so with the tune I am running. Whether running the 93 tune or the E tune, mileage is improved over stock.
YMMV.