The Ghibli is my first leased car. Since I'm basically just borrowing it for a few years, I wonder if I need to put higher octane gas in the tank. Here in CA, we have 87, 89 and 91; I've been using 91, but I'm wondering if I should just save a few bucks and use 87 since I'm not keeping the car longterm. Is there really a difference in performance? Health of the engine?