Well in Cata Blood won't work because it's a tanking spec. So Frost gives you 20% haste for the party, Unholy gives you 8% magic damage, Arms would give you 4% physical damage and Fury would give you 5% crit.

Mmmmm. I think the MS effect is going to be worth more for PvP, BG's or Arenas, than either of the DK buffs. Thoughts?