Altered Time - your #1 World of Warcraft Mage resource!

Can anyone explain why Mastery is so highly rated now for single target?? I imagine it has to do something with guaranteed crits from firestarter and other set bonuses?

For what its worth, I stopped using my Wriggling Sinew. My 875 Horn of valor and 870 Bough of corruption took over, just picked up a socketed 880 Whispers in the Dark from normal Gul'dan tonight, gonna give that a try. Not sure I would spend too much time farming for a Sinew, it doesnt feel as stron...