We used to have our own gas station at the refinery but they shut it down due to cost cutting. When the operators would blend the gas they would put 93 in place of the 87. I could always tell when they had the 87 lined up because it would ping somewhat when I advanced my timimg. If the gas isn't being tested where you buy it from you could be paying for 93 and actually get 89 and run Ok but you're getting ripped off. I'm just being honest about these gas stations especially the small corner stores. You'll know when you get ripped buying low octane gas. If my shit starts to ping, I'll go back and raise hell with the gas station. I haven't had too many problems out of Chevron gas but you pay a little more. I would stick with the larger stations unless you know the owner of the small ones.

As faras your question on 93 octane = better performance, better gas mileage. Oh and don't let me forget = Nelson tune!!