Since I've recently started driving a '92 300SD around for a bit, I see no big difference (mpg gauge is a nice feature). Maybe a wider center console, and more headroom.

I once thought the W140 was massive in comparison to the W126, but they are virtually no wider than the W126 (the American bumpers are bulky even on the sides). I lined my 350SD up with it and took measurements. They sit an inch or two higher though. They have a nice supple ride, and less interior road noise and a tight turning radius. Definitely a solid ride, and not such a big car after all.

They sure don't handle like a near 2.5 ton car. They are very light on their feet, and I have a lot of trouble believing the car weighs 4600 + lbs.

The W126 is a much better looking car, IMHO. But the W140 is not terribly bad looking either.

Not enough of a difference between the two. An S-Class is an S-Class.