i orginally started with a dk tank and 4 shaman in instances. Since then i tried a pally tank and dear god it's so much better. easier cast sequence and better agro managment and even more dps i've found. I have 2 5 man teams and i've totally dropped the dk at this point for pve and i'm testing a druid instead in his place for team 2. Seems to be pretty good so far. Just too much micro management for me in dk's. Fun class, but if you haven't tried pally or druid you should.
i used cast sequence for my tanks. they don't do that much damage anyways so that extra 10% or so isn't a big deal to me.