5.4 - The State of DPS Wars vs. Deathknights (Pve)
What Val said.
More to the point, in the raids I have done recently, the damage leaders have been a completely mixed bag. Sometimes a Mage, a lock, a hunter more often than not but I really don't see any evidence supporting DK's being that much better than warriors.
The bottom line is to play what you want, what is fun and let the chips fall where they may. If you we're at the level of progression concerned with such fine edged min/maxing, you would know the answer.
your hat may be nice, but I have the little white tank top that says Legendary right across my boobs. I win. (or more correctly, H wins)