Having owned W124 300E with the M104 3.2 motor, I would say get the E420. New they were much more than the 6cylinder, but, as stated earlier, they are very closely priced. Don't get me wrong the M104 is great have 145k on mine, never let me down, other than the typical repairs, radiator...wiring harness... head gasket....A/C.... and it still runs past 140mph if I need it to....But the E420 will deliver more acceleration, hands down.
Bilstein HD Struts
16" E420 wheels