I think it's fine as 20 at least for druid's sake. Sejta, Druid tank of paragon on Lightning's blade, EU(6/7 heroic FL) heavily values stam over all other stats too. Mastery is not that great for druids tanks imo. I have 217k hp raid buffed in FL with 37% to dodge and I have been told that I am way more easier to heal than our paladin tank stacking mastery.