I just bought a 2004 V8 Limited. About gasoline, the manual says the minimum octane rating should be 87 but for improved performance they recommend 91. I've never seen anything like that before. In my Hondas they always said simply 87 was the minimum.so I always used regular. In my Audis they said 91 was the minimum, so I always used super. What do they mean by "improved performance" from 91?. What specifically would improve, and does that mean that 89 is better than 87 but not as good as 91? Also what do you guys use? Thanks Dan