The ratings always get inflated at the tail end because teams trade points to boost one team up into the threshold. I would say guess what you think you need and get 30-50 points higher than that to be on the safe side. Ultimately if you want the duelist title as well mark where your threshold is that you can't fall below. It's pretty much gambling at it's finest

Also any value that you see in Hysteria or Vampiric Blood, with your spec you could drop points from the additional snare to grab these, but I'm not sure how crucial that extra snare component is when your already chains of icing.