I like Blood of the North not just for the Death Runes, it's also great for the Blood Strike buff, since you will frequently use Blood Runes for something other than Pestilence. Blood Boil is quite weak if you'r frost spec and aren't tanking more than 5 things.
Also, can someone explain to me this universal obsession with Obliterate?
Even single target my Howling Blast tends to more consistantly do more damage. If you have Rime (can't figure why you wouldn't except MAYBE for your tanking spec) then you have frequent opportunities to Howling Blast then immediately Oblit/DS. And if you're hitting two or more targets Oblit can never touch Howling Blast damage. On top of that, even with a 2-hander I have a 55-60% functional crit rate with HB in leveling greens. For a tank, Howling Blast cannot be dodge/parried/blocked, Oblit can. That's further liability beyond just hit chance.