I have a lvl 69 pally tank and I just started doing northrend dungeons. I havent wiped a group yet cuz I died and the healers only need mana after maybe 6 pulls.
I was wondering if I should stay in my tank gear I have or get dps plate for higher hp until I can get some tank gear?
For leveling, I always go with the idea of "is this piece an upgrade? If so, how much?" LK normals are easymode and your success in them won't depend too much on your gear. By the time you the ICC 5 mans open you'll be 80 and should already starting Cata leveling. All-in-all gear won't matter (much) until you get to Cata dungeons.
Beware if you are in questing and Northrend dungeon gear and head into BRC and ToT it is a signifigant jump in...damage output and intake. You might consider questing and getting some il272 gear and going in at 81. The main diffference is about 20k hp more for your healer to work with, you also dont have to dicover the dungeons anymore so just go quest in hyjal and replace your old gear
As long as your not having threat issues, and your not getting burned down too fast for your healer to react, avoidance is key. My bear has been told he has low HP many times and had not issues staying alive in dungeons, and I'm using as much dodge as I can.
That said, I have just started healing northrend dungeons on my priest and not had too many issues even with tanks that 2H tank, so as Buckwald said, gear isn't a big deal.