Do you lose 4p when you use backbreaker? if you already have 4p, then tier hc shoulders are worse than backbreaker. If you spend few seconds, you will see that the str bonus is minimal and it doesn't give the best 2secondary stats like backbreaker.
If you don't get 4p bonus with backbreaker, then hc tier shoulders are definitely better.
These are just what I figured out by glancing at them but I will get surprised if it turns out to be wrong.
The tier shoulders are slightly better but the difference is so small that it's not worth taking a BiS item away from someone who could use it more (hunter, shaman)