Dont use anything more than regular unless your vehical manual says so. This point has been pounded repeatedly on the internet. You will not get any benefit running anything but 87 octane regardless of any year car that was not designed or intended to use it. Speaking for my car and I might speak for some others as well, with the new style PCM (late 99) have adaptive timing trim. (Well better then 98+ cars anyway) However it is not adaptive ABOVE the timing tables. It is designed so that the PCM compensates for variations in fuel quality in a range right around 87. (Roughly +/- 2)

The only other benefit to running, say 89 octane, in a car programmed for 87 is if you have pinging from carbon buildup and dirty manifolds. However this need for higher octane actually lowers performance and mileage. (i.e. efficiency) While 89 octane masks the problems the real fix is cleaning out the carbon and your manifolds.