I have switched over to Blood DPS and am enjoying it. I am at 20-23% Armor Penetration now which seems to be the magic number to consider switching. My multimob DPS is lower since I don't have as powerful Blood Plague and Frost Fever or the spell love of Ebon Plague and Desecration. My single target DPS is higher and my PVP damage is brutal on clothies. As a side note, my PVP damage on armored targets varies - Scourge Strike is Unholy damage whereas Heart Strike is Physical.