Look, without logs and parses it is impossible to know how much of an impact expertise really has. What we know is that because expertise is on the armoring the item budget for expertise takes away a large chunk of your main stat and endurance, so you basically trade away survivability and damage for survivability and damage, so even if expertise is better it is not THAT much better than pve gear. It really depends on class, take a marauder for example, they heal 2% of their total hps each time one of their dots crits, can you really guarantee that having 12% dmg resistance is better than a much higher hp pool and crit rate? well, i don't know. I know it would be damn close though. On the other hand for a healer class having "stronger" hps because of high expertise is better than having a larger hp pool, because it makes his heals doubly better. The game is still in it's infancy but i have seen people dominate in pvp gear and i've seen people dominate in pve gear. The main stat/endurance penalty you take for wearing expertise gear makes the gap between the two almost negligible.