I have a fairly high performance motorcycle that many have said need to run 92 octane fuel for maximum performance. I decided to do a test of sorts. I checked mileage with my normal 87 octane fuel and 92 octane fuel. I normally run 89 octane 10% Ethanol blend. I started with a tank of 87 to "clean out" the 89. I ride back and forth to work so I used that as my test track. The weather was about the same for the entire test. I checked my mileage for two tanks of 87 octane and two tanks of 92 octane with an extra tank of 92 to "clean out" the 87. At the end of the test I had a reduction of mileage with the 92 octane fuel. It wasn't much and maybe with in the error margin of the test
IMO the 92 had a delayed burn which equates to less cylinder pressure / less performance. Which required a larger throttle opening to make the same power. My "butt dyno" or seat of the pants could not detect a difference in performance.
Is / was this a valid test? I don't know. I do know it cost a lot more money to fill the tank on my bike using the 92 octane fuel with little if any gain. If I had been able to advance the timing of the engine I may have seen a tangible gain.
Take the above for what it's worth.
I don't believe our small engines warrant using anything but 87 or 89 octane fuel. Using the same FRESH fuel from the same supplier every time would be a better bet IMO.