I agree with the others that you're better off spending the extra $3 per tank to get the 91 octane.
But I just gotta say...........$1.74/gal for 91 octane! Holy hi-test Batman! You've got to be kidding me??? We're paying around $2.25/gal for the stuff here in SoCal, so (and I mean this in the most friendly manner) quit yer whinin' and put the good stuff in the tank!
$2.25/gal[xx(]...why those lousy !&^$%*#&%....I oughta
...geez if I could get my hands on.....