Can't see any real advantage to the 600. I think the higher weight of the 600 negates the performance advantage, so it's kind of a tossup between the two. I also have lusted for a 600, but cooler heads always prevail. I do love the 500 and it still has more motor than I have skill.

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95 SL500 Smoke Silver, Parchment 64K
07 E350 4matic Station Wagon White 34K
02 E320 4Matic Silver/grey 80K
05 F150 Silver 44K