Octane number

[CoBeerToad]

I know that 93 is recommended according to the note under the gas cap lid. Around here (NW Indiana), 92 is all that I have found. I'm sure it's no problem. A buddy of mine has a premium only vehicle (Nissan 350 or 370, I can't remember which) and he alternates between 89 and 92. He just passed 100k with no problems. Also when I was in Oklahoma, I went to 6 different gas stations looking for something more than 91 and 91 was all I could find. So I wondered how much different can 89 be from 91?

I guess my question is what are your thoughts? Is 91 or 92 OK? What about 89? Is alternating between 89 and 92 OK? I'll always use the highest available octane, but it's just something I was thinking about on the drive home the other day.