These are two very robust performances, courtesy of John Barbirolli and the New Philharmonia Orchestra. The first bars of the first movement of Mahler's 6th Symphony crash in with a slow, grinding, even sluggish quality which many listeners find unusual, even shocking, compared to the faster tempos of Karajan and the Berlin Philharmonic, and (even more so) Bernstein and the New York Philharmonic. But for me they only serve to bring out the wrenching power of this wrenchingly powerful symphony. When Alma's theme eventually emerges, it has much the same quality, which I found disappointing, because sharp changes of mood are for me a mark (perhaps the mark) of Mahler's symphonies. The lightness which Karajan brings to this theme, in contrast with the opener, is something I miss. But this remains a great performance, and if you're a fan of loud hammer blows, Barbirolli certainly delivers.
The Strauss is in many ways more of the same. I am not the world's greatest admirer of Strauss, however, so I not really the person to judge.
In summary, then: a great if idiosyncratic performance of Mahler's astonishing symphony, which belongs in every Mahlerian's collection. And, as a bonus, a very good performance of Strauss's Metamorphosen.