Keep in mind that while Haste > Crit > Mastery is what is currently simming for single target, the stat weights are very close for crit and mastery so any fight with cleave or aoe mastery will likely pull ahead of crit.
Based on my findings running quite a few sims with various gear levels - Str > haste > crit > mastery. Hybrid haste gems and straight up haste gems only start out performing their strength equivalents when you have at least 4pc T14N. I didn't sim LFR tier so I can't really speak to that.
So, you're saying to gem STR gems in prismatics until 4pc t14 and then go straight 320 haste gems? I was under the impression I should just gem straight haste in prismatics regardless of my gear.