Difference between haste as main stat and mastery as main stat is 0,11 sec casting timer reduction. With Mage Armor on i get 1.45 cast timer of Arcane Blast with haste as main stat to 1,56 Arcane Blast timer with Mastery as main stat BUT the difference in dmg is quite big in bursting/which arcane heavily depends on,similar to sub rogue but caster/. With a lot of testing with haste build all procd burst in arena my top Barrage on full geared leather/for dummy/ player was 167k where with mastery build my top was 211k. Its not worth to loose stronger burst for 0.11 sec casting reduction in spells where you need faster casting timers for 3 spells/Arcane Blast,Polymorph and Ring of Frost/ since u can stop Arcane Missile cast and get charge for free. Also Ice Floes for Arcane is mandatory,yes Blazing Speed is much easier to use but once u got urself a melee on you after this blazing speed you cant do **** for 25 seconds where he will cc/kick every cast of yours,where with Ice floes u can - fake cast for kick,Ice floes,cc/slow dat annoying melee on you and continue your rotation with ease until you reposition urself . Also polymorph while moving...nuf said.