I mostly use 91 because that is usually all that is available in this area. If a higher octane is available it goes in. I seem to get the best mileage and performance with Shell gas whether it is 91 or higher.
Anything less than 93 and I get a ping. When traveling to Sturgis, I carry some of those octane boosters because of the difficulty in finding anything above 89 in that part of the country. Unless things have changed recently.
Not sure about California but I cant find 93 oct anywhere. We only have 91. There is a spot where I found 100 but am afraid to try it. Would it be bad?
I live on E coast FL (Space Coast). I have found two stations with ethanol free fuel. They cater to the boating community. Ethanol destroys the seals in older boats fuel systems. It does give my EG a MPG boast.