[Kajtek1]

From what I know -all MB manufactured in last 20 years have anti-knock sensors, so the engine timing is adjusted for different gasoline.
How the high octane works? The only difference the driver will notice is under heavy load. Since MB generally have much more power, than really necessary, most of the owners will never notice the difference.
Racing from green light, or driving in the mountains is another story.
In US octane difference between regular and premium is minimal. Years ago, in Europe I drove Fiat, that was design for 96 octane. One time I had to put 78 octanes in it. It was knocking on accelerations like crazy (no sensor) so I learned quickly to back off the gas, when I heard it. So using much less acceleration I had better gas mileage at the end.
Then on the trip to Yugoslavia I was able to fill it with 100 octanes. With this gas I was able to drive in the mountains at 40 MPH on overdrive, so in this case I was saving fuel as well.
It all depends what you do.