I have a 500sel '85 and run only 87octane. Everything else is wasting money.
Newer cars usually have electronic ignation with knocking sensors to avoid engine damage. If the sensor signals knocking (premature ignition of fuel/air mixture) the computer will retard ignition. You can do this manually on engines without computer. Get a strobe light and retard ignation a few degrees. Try out until you get an acceptable setting. It'll make your car slower on take off. You may not even feel it.
boili