According to EJ, your basic rotation will be one of these:
1. AB AB ([mbarr] or AB AM) = Arcane Blast, Arcane Blast, if Missile Barrage Procs, Arcane Missiles; if not, Arcane Blast, Arcane Missisles.
2. AB AB AB ([mbarr] or abarr) = Arcane Blast x3, then Missile Barrage if it procs or Arcane Barrage.
It depends on the length of the fight. A shorter fight will use the second one, as it uses more mana but does more damage. A longer fight will use the first, as it still does good damage but uses less mana.
Your hit, as said, is way too high. You need 289 as an arcane mage, assuming NO outside buffs (like a draenei's 1% chance, or misery/improved FF's 3%). In a 25-man raid, you'll only need 183/209 Alliance/Horde (hence Anobix's comment). All that extra hit is worthless. And your SP is obviously wrong.
Edited, Apr 2nd 2009 11:46am by LockeColeMA