Hey, recently I have passed the il 540 mark on my Mage and finally switched to spec I wanted, Fire. Sadly, my dps dropped by a lot compared to Frost (arcane too i guess).
With Arcane Brilliance, Molten Armor, flask and food I barely get 39% spell crit, as only about half of my items orignally have crit on it. I only just start running normals, and as Fire i only went to LFR so far (switched yesterday) so it might be just me not quite getting the spec yet (it's quite complicated compared to how super simple frost is) but I am not sure if the amount of crit fire needs makes it just impossible