I usually try not to post on this particuar forum since I'm a nobody............

but my understanding of low vs high octane gas is that the lower octane doesn't necessarily "burn faster" but is set-off/ignites sooner due to volatility. Meaning, when there is high compression the molecules being packed so tightly, low octane will not handle it as well (detonate on its own accord) as what higher octane will sustain. So high octane has a higher threshold than low compression motor even needs or will put upon it, hence the waste of $$$.

Once ignited, the burn rate is the same.