If tanking/Healing I would say keep your gear around 5 levels of the dungeon. If level 75 dungeon the stuff at level 70 you get from poetics will be fine. Beyond that you might want to put on anything you pick up in current dungeon if you win anything. If not try to get at least 3 pieces before moving to the next.

If DPS...not as important but you will be slowing things down for the others. Poetics can do the job well enough till the next Poetic set but much like I said before...any pieces won you may as well chuck it on. However Poetic is stronger than the early set of dungeons and is roughly even in the 5s. Example being Poetic 50 gear is pretty much even with level 55 gear. Beyond that take the new stuff and wear it.