You haven't said yet, wether you checked/replaced the caps and rotors. I replaced mine at 92k and they needed it. You car's mileage is not that far off from mine, it wouldn't hurt to take a gander if you haven't already.
Those two V8's are quite different. Different injection system, twice the amount of valves, and two caps, rotors, and coils, just to name a few. My 420SEL is said to have 201HP, the E420 has 275. (kind of amazing, isn't it?)
"...rationality of thought imposes a limit on a person's concept of his relation to the cosmos." -Nash
04/71 280SE 195k
09 Jetta TDI