So, just for ha-ha's, I tried a tank of 93 octane in my SE 5-speed. I must admit there is a difference in the performance of the car, mostly in the ability to keep it in higher gears at lower speeds (which I assume is the knock sensor not triggering). I would surmise that this would result in slightly better gas mileage if driven accordingly. Having said that, probably not worth a $.30 or $.35 differential.
2013 Tangerine Scream ST