Well it depends actually IMO anyway

Because 2 weeks ago in SF 91 was like 2.99 a gallon and 87 was 2.79, so calculate 20 cents times 9-10 gallons thats roughly a lil more than 2-3 bucks more and u get 91 octane

But if u like to hold on to ur wallet and dont need the 91 octane then 2-3 bucks are saved

Speaking of 91, i heard that since the B18b doesnt need it, putting 91 actually can hurt ur motor, i doubt its true, but my friend suggested otherwise...dunno