corrola xrs fuel grade

Hi! New to this forum.Anyway,just bought a new 2005 corolla XRS.I would like to know what grade of fuel other owners are using.From what I have read 91 octane should be used.The dealer said it was ok to use 87 octane for normal driving,they even filled it with reg. before I drove the car of the lot.Been driving it for a week now with 87 octane,there has been no sign of pinging or knocking.The car is not driven hard.Any thoughts or expereience on this subject would be appreciated.Thanks.

I would think the computer would keep you from hearing any knock. Do you notice any significant decrease in performance? My mom's Lexus ES300 will chirp the tires with 93 octane, but with 87 it tips in strong then falls on its face until about 3000rpm. No pinging but you can definitely feel the knock retard.

How's your mileage?