Fortress and Void Ray can't compete with their rivals, especially when they're in service to making Mind Flay aoe tick for a little more. At such low values, it just isn't impactful enough.
Here's my setup for 7.3.
I have two gear sets, single-target and AoE, that I'll swap back and forth between.
Single target uses Mangaza's and Sephuz. AoE uses Heart of the Void and Sephuz.
Talents: Cookie cutter raid spec except Misery for most dungeons. Mindbender for Tyrannical weeks only for certain dungeons.