Dragon Soul is supposed to be nerfed starting this week. It will be a 5% reduction in boss damage and health, and that number will gradually increase. It doesn’t affect our attack power or abilities, so our damage output should stay about the same.
For rogues, this nerf has some small effect. It means that bosses will die quicker, so you might not get to use your cooldowns as often. This might have a small negative impact on our damage totals. Be aggressive using your damage cooldowns.
Here’s something interesting you might try. On Ultraxion in 10-man normal mode, the Hour of Twilight does 300,000 damage. Presumably that will be nerfed down to 285,000. If you hit your Feint, reducing AoE damage by 50%, that should only hit you for 142,500. If you’re in 378/384/397 gear you probably have enough health to survive that, assuming that your healers are keeping you topped off. If you’re feeling adventurous, see if you can live through an Hour of Twilight without hitting the Heroic Will.
Of course, if your health is below 142000, or if you time the Feint wrong you’ll die. If you manage to survive, that’s extra dps time. You might give your healers and raid leader a heart attack, though.