What I saw in heroics and normals ranged from 4-9k singletarget tank n spank.
for heroics 7-8 is a must Id say with a solid 4-5k tank in solotarget. Its a close one with healer mana if dps are at 7k but for some reason I cant seem to see any real nukers with 10-13k dps.
Because almost no fight Ive seen so far is purely tank n spank and the DDs manage to do 7-8k Id say you could say they are 9-10k on real matters.