I only have one gasoline fueled vehicle, a 2015 non supercharged Corvette. 91 octane is recommended. While I can afford it, I never like giving the oil industry much more than I have to. In this area, there is a big spread between 89 octane mid grade and 91-93 octane. So I experimented with 89 octane, and the car runs fine. It is direct injected, so the fuel never is in the cylinder for a big compression stroke when pre-ignition occurs. Also, I do not run the car that hard, and during the hottest weather, go back to 93 octane.
As for ethanol, the pumps here say "up to 10% ethanol". That does not mean that all grades have 10%. Usually, the higher the pump octane, the lesser the ethanol. That is because the ethanol has a higher octane boost effect on the poorer octane naphtha in regular gasoline. Some stations in this area even advertise ethanol free premium, but the octane of that premium is usually 91, not the 93 at other stations not advertising ethanol free.