considering there is two encounters in icc that you have to manage adds, id say blood is the way to go. Plus 3.3.3 WoTn looks very sexy. Also, im not sure im correct but 2H frost is pretty broken currently-however i could definitely be wrong. Threat isn't something you would normally worry about, but in my experience with my dk alt I never seem to have enough in my 25 man raids with people pulling 7-10k normally. I love vamp blood, and i enjoy blood tanking. If you are a comfortable on a death knight then blood should be an easy switch for you.