I have alot of trouble seeing an argument for DW Blood or Unholy on live, especially now that frost has talents that specifically support it. If someone can put a build and gearset together and show some success with it, i'm all ears.
Mav: I'm not in ToC 25 yet, but I know several DW frost tanks that are. My threat in Ony 25 as DW frost is fine. I think your question shouldn't focus on whether or not one produces more threat than the other: the question is whether you can produce enough threat to do your job. if blood can put out 10k threat and Frost only pushes 8k, but the DPS never break 7k threat, then the frost tank is no less better off. there is no real bonus to doing more threat than another spec if the other spec can still hold threat, other than making yourself feel more secure.