I own a 1989 300SE and I am very pleased. I have owned a couple. Speed off the line isn't very good, but once you get going, the acceleration is adequate.
I would go for a 420 or 500, but I live in the UK, so petrol and insurance would be a joke.
Get the car checked over before you buy as a lot of the repairs I have had done have been expensive. Especially the A/C. Problems that I have had with all 300SE I have owned have been water pump or A/C related.
Once they are repaired though, the cars sould be good for 500,000 miles.
I love the W126

Oliver

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Oliver