I've run 87, 89, 91, and 93. I wouldn't run 87 long term but I had no problem with knocking when I've used it which I expected because of the anti-knock sensor.
I used 87 a couple times, the car seems slightly sluggish when using 87 and gas mileage drops a bit. I just stick with 91-93 now. I have noticed the best gas mileage with BP and Speedway gas. That's mostly highway miles with a lead foot. Just my $.02
Once after working 28 straight hours I filled up and realized I had put 87 in the tank. It ran without any knocks are problems, but I still always use 91 or better.
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