Because tier gloves have haste on them, gloves have less stats on them than helm, chest, & pants, and you need your 2pc unless you're in BiS Haste build. It's the most sensible solution stat-wise to use tier gloves & shoulders, with offpieces in other slots-- but obviously if you can't get a heroic token you work with what you have.
I and a few others will be discussing the value of crit rating in this and maybe other threads-- this only applies to those with ilvl 580 Purified Bindings of Immerseus because of how crit damage increase influences icicle generation & bomb damage. Please, you, and anyone else reading this thread do not think that crit has a value or place in any stat priority for frost mage unless you are at that gear level. As my guide clearly states, crit's stat weight is insignificant, and you should not be desiring crit on gear or gem/reforges-- ignore crit!
Now all that said - put stat weights into AMR as described in my guide for the mixture build, going to 14242 haste. Then click optimize. I cannot comment on giving up .35% mastery for 1.2% crit because I don't know the rest of your stats. You can trust my guide.
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Really not meaning to be rude but look at this again please: