As interesting as the ending to Boulez's Part 1 is (and loud!), I'd say that Nagano executes it even better. For me, Part 1 is the highlight of Nagano's M8. In Part II, while conducted at equally slow tempi, Boulez definitely has more intensity in the first 20 minutes of the movement than Nagano. However, as I also indicated, the baritone solo - the first solo - isn't all that great. But on the other hand, I really don't like the tenor on the Nagano M8 - that was a big hang-up for me. Botha is clearly the better of the two tenors. Unfortunately, as I also indicated, the penintant women are recorded rather close up on the Boulez. I don't mind a slower tempo either, as long as the women are not covering up the beautiful and interesting orchestral detail. I feel that Urmana is way, WAY too forward on Boulez's "DLvdE", for example (I also don't think that she's half as good as many others seem to feel that she is).
I actually find it easier to focus on Mahler's fabulous orchestration behind the penitant women, if it's conducted at a somewhat more "flowing" tempo. It's hard to get the continuity in the one's mind, if you're just crawling from one orchestral entrance to the next. There's also another problem for me: Mahler's vocal writing is just plain ugly! Clearly, he writes for the penitant women as though they're part of the entire orchestral fabric. In fact, what Mahler writes is really just a slower variant of some of Beethoven's uglier vocal writing towards the end of his "Ode To Joy". Obviously, Mahler's chord changes are more "find de siecle"-ish (turn of the century), but the female voices are doing the same sort of "inverted intervals" business. Let's face it, "Vissi D'Arte" it ain't. But yes, it can be quite beautiful; if the singing is done softly and gently.