Originally Posted by Yörgle

As far as I'm concerned, I recently started to stack stamina and to use SSG rune because we were trying to kill Blackhorn HM and the loss of mastery is worth it, as it lowers the chance of seeing my health bar melting in a second. =) (To be clear : I still used the right gem color to get the bonus, just that I oriented it toward stam. I didn't just use stamina gems.)

I see that you "only" killed Morchok in HM (hope you don't mind browsing your armory, I just wanted to know in what context you were asking ^^) so you should be fine for the next encouters with mastery gems. Maybe just swap your mastery trinket for a stamina one on Yor'Sahj HM.


Regarding mastery cap, I happened to see some TC about it, talking about some inner DR (as avoidance lowers the efficiency of the mastery obviously) but I didn't look much into it yet. My feeling (so nothing very formal) is that the randomness of avoidance make this "DR" disappear as in HM you just want a reliable mitigation (so the biggest shield as possible) when taking a damage spike.
The topics : DS Demise: How blood shield falls behind - Forums - World of Warcraft and The value of DK mastery (math / theory) - Forums - World of Warcraft
(Again : I didn't look much into it and it's quite old so I don't know how reliable it is.)

Finally : there was a simulator (Bloodsim) but it's not up to date.
You can find it by displaying old topics in this section of the forum.