I spent the night doing some math on gear for fun.
I tried to go with actual progression. For example i did not include Heroic Head and Shoulder Tier because those drops from 11th and 12th bosses which i consider being progression.
Tier : i am not aiming for last tier bosses. You take what you can and it is safe to aim for the first 6 heroic bosses. You want Tier Hands + Chest combined with 3 thunderforged off piece. 2 Thunderforged off piece are fine but you need to make sure you get your hands on the legs.
Weapon : main hand + off hand give better result for affliction. Unfortunately those 2 bis drop from Sha and Spoil which won't help that much for progression in my opinion. So we should definitely try to go with Gaze of Arrogance which is already on farm : heroic is fine, heroic Thunderforged should obviously be kept. You get what you can in progression so aim for either a heroic thunderforged staff or a heroic thunderforged main hand.
If you are interested in numbers you can have a look at that spreadsheet. Mainly done with my current gear and stat weights + gear score from wowhead and lootrank.
This is not an optimized gear list. It is a "take what you can get with the early bosses" to kill the last bosses. Once progression is done i believe Main hand and off hand is the way to go (unless you want it simple and aim for a heroic thunderforged staff) and some adjustment can be done with the tier set piece.