Sorry to bring up an old topic again, but I am a huge M6 knut...
My favorites, in no particular order: Zander/Boston, Rattle/CBSO, Barbirolli/NPO, Bernstein/NYPO, Delfs/Milwaukee, and I like Sanderling/SPPO and Zinman/Tonhalle as well.
Barry, you mentioned having a burn job of M6 with Rattle/BPO as the middle two movements...I'm guessing you may have meant Rattle/CBSO? If not, how is the Rattle/BPO performance? I've been waiting for a BPO/Rattle M6...if the Ninth is any indicator, that should be good.