I saw Bychkov give an outstanding M6 with the Vienna Phil. in Berkeley, Ca. I liked much more than the famous Bernstein one, which I also 'saw' on tour at Carnegie Hall. There's a very good DVD of "DLvdE" with Bychkov conducting from Cologne (I think). Tor Kerstin and Waltraud Meier were vocalists, I think. I have a burned copy of it some place.
I think Bychkov is a very good conductor, and is well respected as a guest conductor when he's in San Francisco. However, he doesn't 'pick up the tempo' when making recordings. As you might recall, Fritz Reiner said that you should make recordings roughly 10 or 15 percent faster than you do your live performances. I think he had something there.
Interesting factoid on the Bychkov/V.P.O. M6: he was going to conduct it in andante/scherzo order, but changed his mind to scherzo/andante order at the last moment. Good for him - it worked fabulously. I believe that that is very possibly what happened at Mahler's own last performance of M6 in Vienna. There was a reliable witness to that happening.