Indeed, the PanAm DC6Bs lasted to the mid-1960s, when they were replaced by 727s. This was both on the Berlin shuttle routes and in the Caribbean. meanwhile the rest of the fleet, Connies, DC7s, and Strats went the moment jets were available.
A lot of the DC7/Super Constellations for many operators built as late as 1958, both with Wright engines, were withdrawn within 5 years, and a good number of them never flew again. I believe the big R-4360 Pratts on the Strat were little better.
I believe there is still one DC7 operated commercially by a freight operator out of Opa Locka, Florida, in an ersatz-American Airlines livery (possibly done for a movie). I wonder how they keep it going commercially after 50 years. Picture here :
http://www.airliners.net/open.file/1277662/M/