this is great info. i await your results, but that looks promising and maybe it's something i can try.
i had never thought going to 89 with E10 would improve things over 87E10.
your driving looks similar to mine (26-28mph average on a typical tank which i usually guess-stimate at around 75-80% city in my suburbia type of driving -- hard to pinpoint though as i know some of my stretches of freeway are 1-3 miles which basically doesn't mean highway since so much fuel is spent accelerating up to 65-70 and then i'm back to the brakes and city driving shortly after)
anyway, i think i may have to try this out. it seems you are getting 6% increase in mileage?
that's not bad if it's only 10-15cents more per gallon.