Im only going to be able to touch on points i know about.
for any heroic you will absolutely need 485 def min. 490 def is what you need to be uncrittable to anything.
but 485 is good for heroics.
From what i have seen and experienced is that if you dont have over 11k hp unbuffed its gonna be a hard time and slow instance. before i was above 11k hp, we would get to a few pulls and then after so many tries the group would fall apart. of course some of the fualt is on the dps and heals, but still.
For alot of heroics people want their tank to be around 11-12k unbuffed hp. That way when they get buffed your sitting pretty high up.
Right now for heroics i have never had a problem holding aggro and im sitting with 254 SD. Of course there are times where the mage or something is sitting in T5 gear or somethin crazy and they blow me outta the water.
Ill check your armory out once i get on a computer that will go there. Personally i would recommend the Merciless gavel with the +40 SD enchant on it. that will give you around 260ish SD off the bat. Then get the spaulders of the righteous out of Regular Bot off the 2nd to last boss(Laj). That will give you extra SD.
Overall the main number you need to worry about is your defense being at 485, then get your SD and stam up.
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http://www.wowarmory.com/character-sheet.xml?r=Darkspear&n=Meatydog