I have a '95 Mazda 626 ES which says I should be using mid-grade gas, and therefore it’s what I always use. I did try using regular once and I definitely noticed a decrease in power, so sometimes regular just isn’t the way to go.
Regular grade in Utah is 85 octane.
Both cadolphin and I have California cars which the manuals state require 87 octane.
If we put 85 in our vehicles we notice the difference almost immediately. Sluggish, must downshift more to get up small rises in the road, etc.
But we simply despise paying 15 cents per gallon more for 87, especially now. 85 octane in Utah is comparably priced with 87 octane everywhere else. I think that’s cheating, when Utah reports the price of “regular” as a penny less than nationwide, when actually they are reporting the price of “less than regular,” IMHO.
Yeah, we’re cheapskates.
I started using Shell Gold in my little Honda Civic thinking I’d be doing it a favour in its old age. It started running rough and acting sputtery (technical term 
). When I took it in for its regular checks, the mechanic told me that I should never use anything but the lowest-end Shell in it because it’s not built to use the higher-end stuff!
My dad, the car nut engineer who’s worked for the auto companies had a simple policy about it that I’ve always followed. If it knocks with regular, use premium. If it doesn’t, that don’t, and forget the manual. And his cars always get 200,000 + miles with little to no engine trouble. I’ve never used a car that needed anything more than regular. His Jag takes premium.
7/11 sells gas?