Having 56000 miles of experience with a CCSB F350 on 20's, a shock upgrade will contribute to the ride more than tire sidewall between the 2 choices when I went to Bilsteins was a noticeable difference. It's an 8000 lb. truck there's only so much to expect in ride quality. I came out of a 2001 SD so it's been like 60's Caddy to me.
I'm on the original set of Michelins btw, going to LTX MS2 in the future as they now make it in a 20. If you're near Sonoma County you can grab mine and tow or try it out all you want.
Enjoy Mark