Arcane is a waste of time in a raid now, pretty much 100%. This thread is really outdated since it pertained to level 80 specs and output. 80 = 85? No. Different conversation completely now.
Arcane is the weakest in burst, the weakest in overall dps, and the weakest in mana conservation vs the amount of dps output you can sustain. Hence blizz looking to fix it, because NO ONE WITH A CLUE is playing it.
From a mage that raided through CoT and ICC HM's as arcane, I won't go back - I rolled fire, despite the fact that frost is the #1 DPS spec for raiding right now. The added survival and mobility more than make up for the difference in dps (about 2%, unless RNG hates you) but for consistent, steady raid damage frost is the way to go.
If you can't hit ~17k average in fire and frost on bossfights, you're doing it wrong. (or if you're fire, the RNG might just hate you. Them's the breaks.)

