Let me clear this up. I can't take it. High octane gas burns at the same rate. It is just able to resist ignition more than a lower octane.
Higher octane
unleaded fuel does ignite slower when presented with the same conditions as a lower octane version of it.
Maybe the idea of a "slower" burn doesn't sit well with you, how about a more controlled ignition process. Same energy content, but less volitile under the same conditions, and more stable under harsher conditions, thus making it less prone to pre-igniting.
Slower is just a generic place holder because of the increased amount of input energy required to break the increased number of covalent bonds. aka, Laymans terms to help the average person who doesn't understand the chemistry and physics behind what the real difference is.
This is an article in Motor Trend that explains it.
Here
MIT even gets a word in edge wise.
MIT Here
I can pull up an article from Sunoco and a few other fuel companies if you like.
You have to qualify the type of fuel, and since most of us run on unleaded pump gas. higher octane = slower ignition in the same conditions as lower octane.
Engineered race fuels with special additives or substitute lead compounds, AV gas, and/or actual leaded fuel can ignite at the same level as the lower octane fuels of the same type because they share the same hydrocarbon chain lengths, and the additives affect their anti-knock characteristics. This is also why race fuel tunes and pump gas tunes tend to use wildly different ignition advance profiles. "Fast" burning high octane race fuels will grenade an engine with the same kind of timing higher octane unleaded punp gas can/needs to run.
This is my knowledge from years of ecu fuel and ignition map tuning on race and road applications speaking. I have seen and taken part in some interesting dyno sessions over the years, including one we did to show customers why putting 93 octane unleaded in their 1997 Honda Civic didn't actually add horsepower. In fact, it lost power vs. running just regular 87.