To add on to a previous comment...
Arcane is not Equal to Fire. It far surpasses it.
Arcane lets you remove ALL your +hit gear basically. Right now I have a paltry 9.95% hit. Now add in Draenei(5 per raid, always should have this) that's 10.95% Now add in 6% talents, 16.95%. Close enough to 17%.
This lets me focus 100% on SP/Haste. Right now, as an alt char with zero TotC25 runs, I have 2559 SP, 26.73% Crit, and 600 Haste with NO buffs. In raids my Arcane Blast crit % is 75% and on Jaraxxus I have hit 33k crits with 14k Missiles.
Mind you this is my ALT, not even my main. I can only imagine if this was my TotC25/TotGC10 char...
Fire, however, is not only MASSIVELY dependent on Hit, it just does not perform equally. A few months ago I did Uld10 for fun, we had a 2750 scored Mage, while I was only 2380. I beat him by 500 DPS and he is a very good mage(so it was not lack of skill). 100% Spec based, I beat him even with inferior gear.
Now that I have good gear (2600 score) I have not been out DPS'd on any boss except Twins because I lag so badly with orbs. Even then I'm 2nd or 3rd.
Go Arcane. Like it or not, if you intend to bring the best to raids, it's the way to go. If you play for "fun not min/max" then do whatever you want :) Just want to point out, not equal anymore.