Heres another thought also, what is the best MB spec for a DK main? I think its unholy and heres why:

More PvP utility with reduced death grip cooldown, AoEs, etc
Can still use frost presence to get the extra armor/threat generation for PvE
Permanent pet for off tanking/additional aggro, etc
More AoE for less "thinking" while tanking for 4 shamans.