I have tried out Mastery builds on a couple of fights but really hated the feel of it and in the end, I still took almost as much damage in the long run due to lack of chi for purifying. All it does is smooth out the damage and make it less spikey, but your healers will have to consistently heal you.
If your healers and DPS are good, ie: not standing in stuff then you could do a Mastery build on a couple of fights. My thoughts on Heroic versions only.
MsV:
Stone Guards - Haste
Feng - Haste
Gara'jal - Haste or Mastery. Depends on healer makeup and DPS.
Spirit Kings - Haste
Elegon - Haste
Will - Mastery
HoF:
Zorlok - Haste by far
Blade Master - Haste
Garalon - I prefer Haste
Wind Lord - Depend on your makeup. I prefer Haste on this. However, Mastery would most likely be better.
Amber Shaper - Haste
Empress - Haste
ToES:
Protector - Haste
Tsulong - Haste
Lei Shi - Mastery by far
Sha of Fear - Haste
These are my impressions. Obviously I have not killed the last 3 in HoF on Heroic etc, but we are working on Wind Lord with sub 20% wipes. Terrace obviously normal since it was released this week, but I don't see changing anything from my initial assessment.