Really this post is about BfA and prepatch isn't really in mind but I don't mind sharing what I'll be doing in prepatch.I would first like to say that I don't know how to thanks the effort you guys are doing for the mage community! You are a legend!
I have a question that it's possible that someone asked before but... It would be necessary to wear 4 pieces T-21 and 2 T-20 in pre patch? I always have the feeling that frost mage are stucked and we are not scaling the same way other classes and specs. Maybe with this new build I will start feeling better with the spec. It's just my feeling...^^". Thanks in advance!
Currently, simming all my options with large help from Norrinir's suggestions, I've found out that running TV is optimal due to tier and legendaries. I'm also out valueing tier 20 2 set by miles when using CMS helm and shard. This means my setup will be:
TV /w cms and ebonbolt on st, swapping to SI on aoe or any minor/major kind of cleave.
And my legendaries will be shard and helmet. I do recommend you simming all this on your own character as it might vary from character to character. You can do that by pulling the latest BFA branch GUI or waiting for Raidbots to turn into their BFA setup on next Tuesday morning.