Two things to consider.
One, a V8 W124 may have more power but, it does not handle nearly as well as our I6 motored 124's. How do I know this? Well, I own both. Besides the 500E is supposed to have a sporty suspension and the stock E320 still out corners it. I'm not even going to mention my 300E, it's almost Formula 1!!

Secondly, What's the fun of just buying performance. I think it's much more fun building performance. When I finish my 300E I fully plan on tearing apart the 500E and modding the hell out of it too.

Just my 2 cents!
Adam

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320