Other than the "plug it in the sim" responses, I'm hoping I can get some feel from those that have been in similar situations...
717 Boomkin, 1/13M here. Right now just based on the gear that's dropping I seem to be incredibly mastery heavy. Current stats, buffed:
-3762 Mastery (105.5%)
-1072 Haste (17.5%)
-1010 Crit (16.2%)
-467 Multi (12.1%)
-310 Vers (5.4%)
Won't let me post the link, but it's Kellaris-Mannoroth if you want to armory.
Is it time to switch from gemming/enchanting/eating Mastery to Crit?