I've listened Testament Keilberth. There are two recordings from 1955 actually: "first ring" - Varnay + Brouwenstijn and "second ring" Modl + Varnay. The last one is the best of best! Varnay is Sieglinde, Modl - Brunhilde.

There is also 1954 Keilberth recording with Modl(as Sieglinde)+Varnay+Nilsson(as who?) https://www.amazon.com/Wagner-Walkure-Joseph-Keilberth-Bayreuth/dp/B01G7N441E Heard that it's even better.