I should add that Tony Duggan considered some of those tenor-baritone partnerships in his own 1999 conspectus:
http://www.musicweb-international.com/Mahler/Daslied.htm
I am not quite as fierce a Dieter-detractor as you are, Ralph, but I do find him increasingly hard to listen to after the voice began to go and the mannerisms began to creep in, somewhere between 1965 and 1970. Anything after the mid-70s I find unlistenable. I also agreee that Das Lied is best done with voices as written (though Mahler apparently did not object to the tenor-baritone configuration). My favorites are the usual suspects: Ludwig and Wunderlich with Klemperer, Baker and Kmentt in the live recording with Kubelik, the 1972 Horenstein, with the Bernstein, King, and F-D as a special exception to the rule). Honorable mention to Baker, King, and Haitink (a bit understated, but utterly transparent and beautifully played and recorded) and the similarly cool but beautiful Forrester and R. Lewis with Reiner and the Chicago Symphony.
While I'm here, a thank-you, Ralph, for your extensive opera surveys, which have led me to a number of terrific recordings I might not otherwise have sought out.
Thank you for taking part in the MusicWeb International Forum.
Len Mullenger - Founder of MusicWeb