Actually, both of those specs are not optimal for heroics and aoe tanking, because you're missing some crucial talents that complement howling blast (namely Bladed armor, Glacier rot and Black Ice).
Try this -
http://wotlk.openwow.com/talent#j0EZhxexV0Iz0zfuuAo0x (glyph of howling blast recommended).
With this you'll have greatly improved AoE damage + threat and no need to waste time with DnD. This spec doesn't use Obliterate at all because I frankly it's more useful to spend runes elsewhere (IT for single target threat, Death Strike for self-heals, Howling Blast for damage/AoE). Always try use HB with KM proc.
I generally don't take Endless Winter because in naxx gear 4% str is laughable AP and I don't really care about runic power requirement for interrupt, but if you want to pick it up, swap out some points out of KM.