A couple of things:
1. Does your raid carry a prot Pally? If not, then your threat is going to start out gimped. BoSanc is THE best tank buff in the game right now. With a frost build I able to spam RS and FS on demand for most boss fights when I spec frost. If you dont carry it, your TPS will lag behind your DPS, plain and simple.
2. I would pick up Subversion for the added DPS to BS and OB
3. I would have never thought this, but it looks like (I dont have the math to back this up, saw it on EJ) but specing into Morbity even as frost will help on Single target due to DnD being our best TPS spell at current gear lvls. If you figure out how much a normal OB and BS hit for, it has to over come something like 12K Dam to out threat just one DnD. IDK about you, but mine dont do that yet. Im still trying to get into a habit of dropping DnD on CD. DnD is a constant 600 ish (2.8K AP) when its up.
I cast the spells that make the people fall over.