@TripleF_67 My disco runs fine on 87 I just get better mileage on 91, and she seems perkier.

 

Just chiming in, to well, chime in... Here in Oklahoma, our usual range is 87, 89, 91. Some stations will carry 93 Octane. Usually the price difference is about $0.20 jump per level. There are a few stations though - particularly one closest to my house that jumps their premium (91) about $0.90 more than the 87 octane. My wife currently is driving a 2014 RR Supercharged. I usually will use 91 in it, but on occasion will fill up with 89 - especially if we're taking a longer drive.

In our old D2's that we had, I'd fill up with 89 on most fill ups. Tried to stay in the middle ground, telling myself I was getting the best of both worlds.

 

in Tulsa you should have a few stations with no-ethanol premium. my D2 and p38 always got better mileage by 2-3 mpg when i filled up with that.

 

I've run 90 octane pure gas in my truck but it felt sluggish. Runs best with 93 pure gas but that's pretty expensive but not worth it IMO. My everyday gas is 93 ethanol blend and my truck runs fine. Much better than the 91 I used to buy in Nevada IMO.