Oldest misconception going, that old octane thing.
In the simplest of terms, less power/btu available per unit the higher that the octane goes, if nothing else changes.
What higher octane has going for it is that is less combustible, less susceptible to detonation allowing more spark advance, higher compression, better cam curve grinds, etc without inducing knock.
Just putting e85 in a regular car will almost certainly get you instantly out of the knock sensor/spark advance/o2 sensor window.
I've heard a story, in some variation, a thousand times of "My buddy and I would go to the airport and fill up his Chevelle with AV gas and then go kick everybody's ass racing"
Unless they re-jetted and and dumped in a ton of spark advance, just for starters, they got worse performance and are nothing but lying idiots.