I have had mixed experiences. The first one I did Our group consisted of 4 level 51's and my 2 toons at 57. 2X Shaman, 2X Pally, Cleric, Ranger.
We did very well, but the mobs were very weak. The next time I went back we had 3 level 51's, 2 level 57, and a level 58.
Dot I believe you were with us this time, playing Dotlbe.
We wiped, and the mobs had been upgraded drastically. The first time with the more lower level in the groups, the mobs were hitting for 180ish. When we went back with the higher average group level, the mobs were hitting in the high 200's. Which if your tank is level 52 or so is quite a lot.
Anyway, I want to see if I can handle them now, the XP was delicious, and it is always free unlike PoI.