Have had my SD up to 95 going across Idaho, and felt solid as a rock. If I had a gas w126, I could see 100+ being very comfortable. The diesel just revs too high at that speed to make me want to do it very much.
Had a '67 Chrysler 300 a few years ago. That 440 engine is an amazing hunk of iron

I pegged the 120mph speedo more than a couple times, and felt very comfortable. Now the brakes on those old things is another matter!!