Yep, I love the W126 but they ride like crap. Total crap. You can replace every suspension part under the car(I did) and they still ride like crap.
You feel every bump, yet during hard corners the suspension is soft.
Its a 1970's design and technoligy has moved on.
The W140 rides as the W126 should ride. I'm still amazed that a W140 with 18in wheels and low profile tires can soak up bumps far, far better then my W126 can. A modern high end luxury car rides and handles many times better than they do.
But I have figured out what my W126 rides like, an M3.
Just without the "sport".