OP, if threat is REALLY your problem, try this:
Instead of using all your Death Runes on Heart Strike, use them on Icy Touch instead. Do this, and gain an easy 11k+tps. Also, don't forget to grab the IIT talent for the extra damage.
Edit: Also, for AoE tanking, and PURE AoE tanking, I could advise you to take an Unholy full AoE build, which nets more TPS on AoE than even frost, at the cost of no real snap aggro. (Don't flame me for this, let it sink in, unholy tanking is good for trash, when you don't need snap aggro. For single target it's poop, I know this.)
http://www.wowhead.com/talent#j0vMZhxZcghI0cbt0zx0uIq <-- A lil talentbuild centred for aoe tanking.