Sub feel pretty OK in there unless you aggro a pack of strong mobs that hit hard. I didn't have time for layer 6 or any layer in coldheart interstittia on rogue, but my xp so far having L5 Skoldus hall and evreything before that in weeks 1-2:
With stealth crit legendary regular mobs die in 2 hits (shadowstrike+eviscerate), elite ones can take 5-7 hits, floor bosses die within 1-1,5 shadowdance, rares take slightly longer. my complaint as rogue would be that anima powers are actually kinda lackluster, nothing too impactful, or I'm just getting bad rng, but the common power of finishing moves buffing CP generators fun during shadow dance.
Did both wings at L6 as a lock, destro and affliction. Affliction felt better, but again, no decent anima powers. Voidwalker even with buffed hp isn't a great tank at that layer. Wiped several times on L6 coldheart last boss due to not getting procs on my anima power (malefic rapture has a chance to give 5 soul shards) with it not proccing at all during 2-3 attempts. The one attempt it started proccing, it was a kill.
Overall didn't feel a big difficulty jump, just had to do much less aoe pulls, so I presume layers 8 next week will go relatively smoothly.