What are the benefits of tier 4 piece frost and crit rating?

[Aégwynn]

Hello.
I am mainly an Arcane mage but I like to keep my other specs viable but mostly Frost. Is it really worth keeping up the 4 set from the tomb of Sargeras with Brain freeze reducing the cooldown timer of Frost orb or should I focus on my item level and stats since my item level is higher when only having the 2 set part working. Also I have been seeing that I do not actually need to get 33.34% crit rating and guides says its not absoulutly essential and I see some high raiding mages who do not have that amount.
Peoples thoughts?

[Xinder]

1. There's a Q&A Subforum that your question could be in to get more visibility by people looking to answer questions.
2. Sim yourself. Raidbots.com makes it easy. You'll find the 4pc bonus is almost always going to be worth it. Maybe if you're talking 30+ilvl differences on tier gear to the non-tier gear then maybe you'd see something. Most likely though you'd keep the 4 pc.