Your current spec is much better, mainly because it takes Bladed Armor (which is a huge amount of threat). There are only a few changes I would make - first, replace Hungering Cold with Deathchill, as Deathchill is fantastic for burst threat (especially coupled with Howling Blast) and Hungering Cold is damn near useless in PvE.
I would also consider getting the Howling Blast glyph instead of Frost Strike for farming heroics - I wouldn't use it single-target (dual disease buffs your Obliterate and Blood Strike quite a bit), however it really helps with burst AoE threat. Instead of dropping DnD and then spending 3 runes applying your diseases to all the targets (generating little burst threat in the process), you can drop DnD then Howling Blast then Blood Boil and mobs will stick to you like glue.
You're heading in the right direction, gear-wise (you're uncrittable at least), but you definitely need to replace that pvp and dps gear. There are nice tanking bracers in H OK and H CoS if memory serves, and a decent cloak from the Wyrmrest quartermaster.