I leveled 88 and 89 killing the water elementals inside the jade temple. Not the dungeon, but the instanced version you enter while questing. I believe you need to be on this quest chain to enter http://www.wowhead.com/quest=29931
I was getting 5.3m xp per hour when going full speed with guild banner down using a 4 man group. Mote drop is good and not a lot of competition since only other ppl on the quest can enter the area.