New entry on the OP:
Q: Haste or mastery!?
A: The general rule of thumb is this: with 1 RPPM trinket, mastery is slightly better; with 2 RPPM trinkets, haste is slightly better; with 2 RPPM trinkets and Legendary Meta gem, haste pulls considerably ahead. However, mileage may vary, so consult with Shadowcraft to be sure.