We live in Mild weather in Northern California with some of the highest gas prices in the nation. I have not noticed performance difference no matter the octane rating, so I generally us 89. I find that using 91 Octane I get a lot of soot on the tailpipes meaning the engines must not be running as efficient as it could. Has anyone else had this experience?I know this is an older post but very relevant. We have a 2018 Envision with the 2.0L Turbo. When we first got it I tried a number of different options. The dealer told me that the manual recommends premium but it will run on regular. Premium fuel or higher octanes are designed for higher compression engines and do not prematurely fire causing knock, their formulation causes combustion at the higher compression. So, I tried 87 octane fuel from Shell, Exxon, Mobil and BP and all regular fuels I tried have a noticeable degrade in performance. Now I know the car's computer is supposed to compensate for all this however the difference in performance, as well as the occasional knocking, and I do not accelerate hard, are not worth the savings to me. I even tried every other tank full and a few tanks of mid grade fuel from the same brands and was still disappointed. So I only buy premium fuel, which the car performs admirably with no knocking or issues. I know it is more costly (although fuel is currently reasonable in price right now, prices are relative when I started driving in '71 I paid 21 cents a gallon at Gas Land for gas and our new 72 Ford Gran Torino was $3,600, a fender on the Buick) however, to me it is worth the piece of mind that I am not potentially damaging the engine (knock) and I can count on the performance. It is a net/net for me anyway as I traded in a '14 Equinox with a 3.6L V6 so where I saved on that with regular I am more than making the higher cost premium up in much better mileage on the Buick.