Not sure about the 50's or 60's, a bit before my time. I can tell you that the propagation during the late 80's and late 90's was really good. I became a ham in 1992, but listened to a lot of DX on the scanner and shortwave radio around that time. I clearly remember sitting out in my car one summer afternoon in 1998 and working Guam, Japan, Australia, and New Zealand on 10 meters using 25 Watts into a mag mount antenna on the back of my car. I had a 10 meter dipole in the attic of my apartment in Lexington, Kentucky in the early 2000. Back during 2000-20001, 10 meters was open to somewhere on almost any given day. I used to work skip almost every day using a stock Cobra 146 GTL SSB CB radio in my car when I was a high school senior back in 1992 before I got my ham license.