Arcane vs Fire vs FFb

Now i was wondering which is the best when youre pretty geared? So far im 5.4k gearscore and playing arcane mage, I can hit about 8k dps on a raid boss. Should I keep playing arcane mage even when I'm bis or is there a certain point where I switch specs? Ive heard from some people that say once I hit 6k gs to switch to ffb mage.

Its not a matter of ur GS but of ur crit rating. FFB and Fire mage require a certain amount of crit or u dont get enough hotstreak procs.
I havent played mage on the new core but as far i know fire ttw is supposed to deal the most dps in high end gear.

Fire is doing half the dmg, so don't even try it.