What your risking is poisoning the cats, which you will find out to your dismay, during your next Smog test, &/or a partial or complete meltdown of the cores, accompanied by a back pressure condition that will gradually interfere w/ proper valve closure function. I have seen Cat's (mine) glowing white hot. That was even after it exploded.

A little background on that: I was given a new Ford truck w/ a company gas credit card. So, thinking it ain't my money, I ran 93 octane from the day it was new. Bad idea.

I later found out through research specific to our engines, that they are specifically engineered (if stock) to run on 87 octane. Octanes above that (stock engine) consistently leaves incompletely detonated fuel that if not deposited as residue on the combustion chamber surfaces, expels through the exhaust valve port.