I don't think that 92 octane should cause any of your problems. i use it regularly with my 1995 E420 and it runs great.
Some possible causes:
1) You ran your tank too low, and the fuel pump picked up crud that is clogging your fuel filter. Have you had the fuel filter changed on the car?
2) Perhaps your car needs rotors and caps early - and coincidentally decided to start acting funny now.
3) Engine Wiring harness?
These are listed in order of likelihood. By the way - the car should never knock - as it has knock sensors that will retard the timing to account for any gas quality. You could run 87 octane in the car with no knocking - the car would just adjust timing - and you'd get poor performance.
1995 E420 (living through an evaporator repair)