The only thing flatter is the US womens gymnastic team in Athens
Drive about 350 miles south of Chicago (still in Illinois). The area around the Shawnee National Forest is hilly.
I can tell a marked difference in performance from 89 octane wth ethanol to 93 octane without ethanol.
To maintain steady throttle pressure on one hill in particular:
65 mph at the bottom of the hill = 30mph at the top with 89 octane.
65 mph at the bottom of the hill = 40mph at the top with 93 octane.
I have never used premium in a car that did not require it. In fact, we have used regular in my wife's 2000 Maxima that does require it. We bought it new and it now has 98000 miles.