After looking through so many threads i still cannot find the answer when to stop stacking haste in favour of mastery, at the moment im at 16859 , im thinking its too high looking at others stopping around 1400 or so.
I don't pay a whole lot of attention to the breakpoints as haste is so variable in an encounter (lots of meta gem uptime, icy veins etc).
Up until very recently, I gemmed Briliant/Reckless/Veiled, but I have been shifting somewhat to Reckless/Quick/Lightning gemming with new gear. Haste gemming is certainly better than intellect at this gear level when not haste-capped, but the meta gem in particular will easily cap instant casts. Akraen has a lot of analysis on haste/mastery balance. What works for you may depend on your latency, reflexes, play style and of course the encounter itself.
A big part of why haste works so well for Frost is that it increases the number of Brain Freeze procs. Bombs will tick faster even after Frostbolt is capped.