This is a bit of a necro. I ended up going with fire/arcane for no other reason than fun factor. It feels like it does better damage than the frost specs i tried..but the visuals and sounds of adding blastwave into the rotation, the occasional stuns and killing bosses faster, all adds up to make it feel more rewarding for me.

This is the spec im using based on a guide for best non-raiding fire spec. Its mostly for single target sustain dps, but the aoe is still more than good enough for dungons. ( its becomes best for raiding after ZG-AQ-NAX due to less fire resistant mobs)