If you want to stick your head into a snake pit, just go to the Mahlerlist, and challenge those guys on the M6 order movement business. Then point out that there are, in fact, all kinds of, "against the rules" stuff that goes on with Mahler. One of them is this: "Waldmaerchen" belongs to the first version of "Das Klagendelied", and not the revised version. Yet, nobody has squaked about the ongoing practice of doing "DKL" in a "hybrid" version for decades. In the first version, the Wedding Piece (Hochzeitsstuck) has a series of fun sounding tam-tam smashes near the start, as well as a big crescendo on the tam-tam at one juncture. The first version also calls for 11 different vocal soloists. On the Nagano recording, they use four "big-name" soloists, plus a number of soloists taken from the Halle Choir, as well as two boy soloists from the Wienersaengerkanben (Vienna Choir Boys)! In the first version, Mahler asks for six harps, as well as all kinds of unusual windband instruments. On the Nagano recording, it's hard to tell if much effort went into replicating Mahler's original specifications. A Db flute, for example, may not sound terribly different from other flutes.
In many ways, including "Waldmaerchen" with the revised version of "DKL" is like doing the revised version of M1 with "Blumine" reinserted into its original, second movement position. Along those lines, one shouldn't reinstate the third hammerstroke into the finale of M6, unless they also do the orginal orchestration that surrounds it (or at the very least, the couple of bars that lead into it). There are subtle but significant differences in how that particular measure is approached in the two versions of M6.
In M7, MTT's earlier LSO one wasn't nearly so frantic sounding in the first movement. On the SFSO one, it's just absurdly fast - far faster than the bulk of the finale. The first Nachtumusik had far more atmosphere on the LSO version as well. On the SFSO version, it's incredibly plain-spun and literal sounding. I do like MTT's more nutty sounding tempo contrasts in the finale of his SFSO M7. But the bright, "Star Wars" sounding brass of the LSO are practically ideal for that movement as well. On the whole, I prefer his earlier one. I also prefer his earlier LSO M3 to his increbidly boring SFSO one. That's just me - I don't like slow, "Parsifal" like renditions of what really is, on the whole, the crown jewel of Mahler's early "Wunderhorn" period.