As previously noted, I'm not a math geek so I am not going to argue BiS (best in Slot) with the maths here. Rather, I am going to discuss your gearing up opportunities by boss, to help you prep your wish list. If you want to see BiS across all available 10-man and 25-man raids, including ICC hard mode boss drops, shadowpriest.com has an excellent list. With more math than you can shake a stick at.
Words of Caution: As with ToC, you will want to be picking up some haste gear from ICC which means doing the hit-swapping dance, so don't be quick to shard or sell your existing gear when you receive an upgrade. You will likely have to swap gear around for raids to ensure you stay hit capped.
Your boss-by-boss gear guide, after the jump.