Well, let's put it this way: the 5th symphony is the one that requires the most 'intervention' on the conductor's part. That is to say, it requires the most 'gear changes' - tempo modifications within a movement - of any of the Mahler symphonies. Vanska did some 'unusual' things in regards to tempo relationships within movements, although most of what he did worked just fine for me (such as the start of the second movement). There will be less opportunity for him to be quite so controversial with the 6th symphony, although the trio sections of the scherzo movement do require precise conducting of the various meter changes (alternating two and three beat patterns), as well as sudden shifts of tempi that are indicated in the score.
Vanska's 12.5 minute timing for the Adagietto in M5 ruffled a lot of feathers. I would have preferred a shorting timing myself, although I found it interesting for a change. The same people won't say a word if Vanska drags out the slow movement of M6 to 17 or 18 minutes, although it's clearly marked "andante moderato" (with no mention of "langsam" anywhere).