That's almost the spec I'm planning on 80. I think I'd go with ... 3 points off Cruelty and into Armored to the Teeth. The impression I get from the others here is that 3% crit isn't that big a deal considering you're cruising at at +15% to all your important abilities anyway, vs. +attack power. Then again, I'm not 80 yet, so I can't vouch for that 100%.
You may also be able to drop a few points from prot (3 exactly; I understand that higher level tanks consider dropping points from the first tier shield talent, if they've got enough SBR) to get AttT, cruelty, and impale maxed (my plan).