I was running around 26% haste, 35% mastery and like 2% vers for a few weeks while we were finishing up Normal and getting into Heroic. I felt really squishy and my SB uptime was around 75% (closer 90% while boss tanking). I switched to Vers/Mast and I feel a lot sturdier. My healers noticed a big difference too. I'm currently sitting at 13% vers and 39% Mast. Of course the game play is slower and more monotonous (I really don't like it), but I'm not dying. Many times our Guardian (ilvl865) dies before me (i'm ilvl859).