Hi vs. Low Octane? What I can say is back in the day (late '80s) when Amoco Ultimate -- the good 94 octane stuff -- was a mere $1.50 a gallon, I would add several gallons of it to a tank already filled with mid-grade, just to see what would happen.
Doesn't increase performance, huh? BALONEY! Did wonders for all my rides! In those days, I lived on Mount Washington, across the river from downtown Pittsburgh, overlooking the old Three Rivers Stadium. The Ultimate made my cars go up the hill to get there WAY better!
But of course, there weren't nearly the electronics on board. Two of my rides had no electronics at all, save for the electronic ignition on my '74 Firebird. Perhaps due to today's fuel-management systems, there isn't much of a noticeable difference -- but that isn't the fault of the fuel, but of the electronic programming.
