My truck refused to run on 87, grumbled at me about using 89 and really shines when I run 92. It hates ethanol and the winter blend we get here.
After doing the intake, exhaust and tuner; and using 92 octane, my highway mileage is +4 MPG. I can't attribute that to just one of those mods or just the fuel alone. I think it all just works better together.