Well, how about the 1951 Bayreuth performance of the Ninth. Furtwangler / Schwarzkopf / Edelmann / Hopf and Hongen. As much as I've always loved your van Karajan choice, Art, the Bayreuth performance (this one of the two recordings, both of which are wonderful) knocks me out and to have been there must have been unforgettable! But, if we are allowed to dream, how about having been on May 7, 1824 at the Kärntnertortheater in Vienna???
