I've MT'd everything so far and have really been enjoying BT/MH, we've got Teron to 35% and Azgalor on 1% since getting attuned about 6 days ago but I'm getting a bit worried.
EU Armory isn't working atm, my (UD) Warrior has 21.8~ hp, 19.4k'ish Armour, 27% dodge, 17% parry buffed. I'm finding incredible avoidance streaks which has basically caused me and our dps no end of fustration.
I've gemmed/enchanted STA and went after AC/HP gear mostly and my TPS with rage is fine (I have about 5.5% Expertise and 4.5% hit) but I'm not sure what to do in future with upgrades like the Teron gun, hyjal cloak.
Without access to your armory to look at your gear piece by piece it's hard to really give a good response to your question, but I guess I'd have to say, regarding upgrades: you should wear them.
The worst part about BT/Hyjal gear is you go from having a LOT of block value in your mixed t5 setup to almost nothing after a few pieces. The bright side is, your threat probably won't start to seriously fall behind your dps until your raiders start getting 4 piece t6.
The bright side is this shouldn't happen until you've significantly progressed into BT, and if you're lucky with drops then you'll have a lot of the good offset pieces that have a lot of block value on them.
When you do develop threat problems, throw on some 2% threat to gloves and just let your dps know you need more time. Ask your raid leader for windfury totem (especially the melee group with an enhancement shaman and feral druid if you run with this sort of setup). These small increases do actually help.
As for avoidance streaks, they happen sometimes...it's inevitable if you wear real tanking gear and not like resilience/offset threat dps rings etc. like if you were to tank with a Garona's Signet for example.
One last piece of advice: if you get above 540 defense you need to consider dropping points out of Anticipation and putting them to use elsewhere. I mean everyone loves defense but it just gets to a point where you'd be better off putting them into finishing Improved Sunder for example (especially after the change to Devastate).
Again, if you can post your armory or at least just a grocery list of everything you wear for general purposes (not specifically your avoidance or TPS set), it'll be easier for people to help.
All I can say from experience is that once you kill Illidan and have access to gear off every boss, the balance just kinda falls into place naturally from wearing as much gear from BT/Hyjal as you can.
We killed Archimonde & Teron Gorefiend but have been quite unlucky with drops.
Atm I am hopeing to get T6 gloves and helm soon.
I've gotten a few upgrades recently and I've mainly seen my block value drop a lot and my health dropped a bit. Mainly my dodge has increased a lot.
The first thing I'm thinking of doing is replace the +8hit gem in my gun with a +15sta gem, if I can receive one from my guild. Usually those gems are for BT/MH gear only.
Any advice or comments on my gear/gem/enchant choices ?
Do I need to focus more on avoidance ? more on stamina ?
There are so many possibilities and different fights that I have a hard time making choices.
Expertise makes a huge difference. That's the threat stat now, not block value.
I'm about the same place (4/9, 5/5) and making the change from high block value to high avoidance takes some getting used to. I had a fun go on Terron where he hit me three times in two minutes. It was really frustrating, but with a decent amount of expertise and +hit, you can still put out a ton of threat just keeping your main hand swinging. Since I was so conscious of being so rage limited, (and windfury was procing a decent amount) I could keep up in TPS pretty nicely.
I farmed for the badge neck, cloak, bracers, belt and pants before we got attuned to MH/BT (I really am incredibly unlucky with tank drops, -never- seen Gruul shield, Lurker Mace, leo belt, kara neck, al'ar cloak, solarian boots as well as 3-4 other upgrades) to replace some ghetto T4/kara stuff I was wearing and all the drops I could see basically had dodge (Naj'entus Bracers, Akama boots, hyjal cloak).
I switched some gear around, Morogrim ring for Hyjal rep ring etc and had a much easier time. Teron and Azgalor dead this reset. Hoping for the shield on our 3rd Kaz'rogal kill to upgrade my S2 shield (/cry)