This is always an interesting topic to discuss. in reality, the higher octane numbered fuels are not as combustible as the lower numbers. This is to prevent pinging knocking and engine damage associated with same. The lower numbers burn better, but can produce detonation. A lot of this is very scientific, but for me, I have used regular unleaded 89 RON for quite some time in my 300E, w/o any ill effects and excellent emission numbers. Also seems to run smoother. I think the effect will be different for each car, but I am happy and have saved a few pennys over the years.
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.