We have 91 No Ethanol, so run that during winter to minimize condescension. Totally unscientific, but got 22+mph over 25 miles on the last tank (highway). When the cold breaks, will go back to 89. Most economical and engine rated.
I played around with this for a while keeping track of gas mileage around town over the course of several tanks and on an extended trip. I found I got about 2 mpg more with 91 over 87 octane. I live 5 minutes from Costco where the 91 is only about 15 cents more than 87 so on a tankful with the better mileage it’s almost a break even cost. Also, maybe just me, but the truck seems to run better and less engine noise with 91. I’m hooked on 91 from here on out.
Ran 2 tanks of 91 ethanol free, then 2 tanks of 93 W/10% ethanol and now ran 4 tanks of 87 W/10% ethanol and see the 87 is putting up the best MPG. Winter blend and single digit temps are probably screwing with my MPG number a bit. I will probably settle in with 87 since mileage will be slightly better and the cost is about $8 per tank less.