I have a London (Decca) 2fer with M1 (Israel PO, 1974) paired with M3 (LAPO, 1978). The M1 is pretty good and the M3 is excellent. The timings of both symphonies are amongst the fastest ones that I own. M1 without Blumine: 14:42, 7:14, 10:57, 18:22, and M3: 33:07, 10:21, 16:40, 9:37, 3:59, 23:16. Maybe Mehta played Mahler more slowly (like Bernstein) when he grew older, I haven't heard anything from the last decade or so.
As you say, there is nothing like a live Mahler, you are totally surrounded by the music and the only thing you can do is let go and enjoy, my last was M3.
Roffe