I've run 87 almost exclusively since I bought my VX new in '99. On the few occassions I've experimented with higher octanes, I didn't notice any better performance and actually experienced a decrease in gas mileage. I have running into knocking a bit, especially as my VX has started to get a bit older (I'm at 90k+ miles), but the brand of gas I buy seems to make a difference, so I try to avoid certain brands (ARCO in particular seems to run pretty poorly).