id suggest getting the 500 int gem and 4pc tier, else arcane seems lacking to me. the thing with 4pc is that 10% is actually A LOT compared to combution/IV timers that you prolly wont end up utilizing the fullest.
While I agree the 4p for arcane is great and better then it is for fire, it's not like you won't do well without it. I am still in non optimal fire spec gear with only 2p and playing arcane I am having great success and on average doing more dps per fight then I was pre 5.1 fire.
Jobahlie-Mage- Only of it's kind since Vanilla WoW