What should I buy first with frosts?
I was thinking about getting the t10 helm because I have the sanctified coin, but I do not want to lose my expertise. I was also thinking about getting the cataclysmic chest.
Here is my armory link:http://www.wowarmory.com/character-s...s&cn=Ilikecake
I dont tank on a pally so cant comment on the best pieces for you, but i can say that you shouldnt need to worry about your expertise, most end game tanks are able to hold threat off 6k+ gs or 12k+ dps raiders, with only 10-18 expertise. As a pally you can hit the bottom end of that just with a glyph.
Outside of that i would look at where your issues are. If you are having problems staying alive go for the pieces with armor and stam, if its threat look for the ones that will up your str the most. If i had to choose personally i would say the chest piece. It covers any expertise issues you could develop, plus it ups your defense rating almost by enough to pick up the crafted legs. Believe it puts you at 66 defense rating over the magical 689 number, where you will lose 80 with the legs (not taking your resilience into account). The crafted legs would be HUGE for you!
I agree with the chest recommendation.
As you are starting to tank ICC25 regularly, I would imagine you will pick up the Broken ram skull helm from Lady Gaga sooner or later so having a T10 helm is less attractive.