I created my 5 man DK group when WotLK came out. With the RAF I was able to level them to 60 just by doing the DK first quests. I still haven't decided what talents to put points into. Even without talents though my DK's can basic round anything they come in contact with.

I have to agree that going unholy seems like it would be the best talents with a 5 man group. Especially against casters.