Using this calc A list of useful Tanking Formulas for Warriors - Dodge, Parry, Block you would need 516 defense. So one defense gem or something to make up the difference.
Furious Gladiator's Greatsword - Item - World of Warcraft
I got that and i believe it gave me .98% less chance of being crit
Does that make me able to get rid of my Stoneskin Rune?
My armory never has my tank gear. But let me know if thats true because id love to gain 4% parry
By going with Swordshattering you would lose the 2% stam bonus from RotSG. The arena weapons are the best EH tanking weapons in the game. I would suggest you continue the EH theme with Stoneskin.
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Agg's tanking guide