just use what the manual says. you might not hear detonation but it does occur. also you might not get as much mpg as with the super so it could be a false savings. also mercedes has no system that adjust timing for the fuel you use. some will change the timing if it detonates but this is not to be confused with changing timing for the gas. you do not want your car to detonate.
its a hint that bad things are happening.

george