Although now you've lost a Decimate because there's no SE, and you're sitting at 4 stacks. You could probably add it back in, but in that case you're pitting a single, unbuffed Overpower against 9 seconds of caster burst. You could add another Overpower to try and play it safe, but now you're going into your "burst" with 260 less TP.

Just let your DRK tank it and use the freedom from tanking responsibilities to maximize your own AoE dps. We both lose a lot more from the WAR tanking in AoE situations.