I play from Australia (so i have 200ms with lowerping) and I find it near impossible to play with stacking crit/mastery as PvP frost. When I made a set with no haste im always accidently hitting buttons that haven't come off GCD yet. When I get a full +haste set...that doesn't happen...and my playing ability is so much smoother/cleaner.
Are there any top rated glads mages that actually stack haste? honestly...feels awful playing with the FULL gcd timer...my brain/hand movements is so use to playing with a quick GCD.
I am always in a comp with a rogue so i always have the 5% crit, why not just get all haste?
Haste is still a strong stat for frost mages, probably as strong as it was in wotlk. Although it's worse than crit/mastery and I doubt you'll find a top rated mage stacking haste.