Yes, the live version is quite spectacular, I believe it was filmed during the celebration of the Concertgebouw's centennial. It's much more of an event. I'm afraid I haven't heard the studio M8 in its Pentatone incarnation, I will look in to that.
I find myself to be more sympathetic to Haitink's first Mahler cycle. At first, I loved it, but gradually I found it to be a bit generic and lacking in charisma. But in recent years, I felt its lack of histrionics can actually be an advantage. This is music that doesn't need to be in your face the whole time. I especially like Nos. 2 and 9 in this cycle, again not because they are heart on sleeve, but for their sheer musicality. And that’s something we never should take for granted.
I’ve heard and read some very disparaging comments being made about Haitink and especially his Mahler. All in all, I think he was a great Mahler conductor. His personality wasn’t exactly tailormade for this music, and he kind of inherited the Mahler tradition through the Concertgebouw's past, but I think he has acquitted himself very good, all things considered.
Kind regards, Shawn