For the rest of 3.0/Sunwell farming, you can gem whatever you want. Avoidance/survivability is trivial now because Radiance was removed, and the other bosses who weren't affected by Radiance, now hit for less. I've replaced my red gems with stam/str just for more threat, and kept my blues as straight stamina.
I generally wear a lot of threat pieces in Sunwell now, capping expertise, capping or near-capping hit, and the rest being good tank pieces. I haven't really worn 4-piece T6 in a while, I never found it really worth it.
The week of Wrath going live I'm resocketing/re enchanting all of my gear for Defense, because we aren't raiding that week, and I'll be using it @ 80 for a while, so I need all the crit immunity I can get.