How about in PvP or would something like Thrashing Blades or Torment be better?
What spec are you running for pvp, full Deception or Wakajinn? If you are full Deception then just get 8 in the Madness tree for Chain Shock. You won't be Thrashing at all so don't worry about talents that buff Thrash.
If you are running Wakajinn then Thrash is you main filler ability and you can be using it quite a bit. Claws of Decay in my opinion is a must for anyone that uses Thrash as their main filler. Torment is not that big of a deal but since Parasitism and Oppressing Force are useless for Wakajinn spec you will be picking up Torment so you can get to Claws of Decay.
I strongly recommend reading the guide that Wakalord put out. He breaks down quite a few specs for you and gets into what talents are worth getting.