Just thought i'd post a tip which i think is usefull as a PvE arcane mage -
Well I found out that when you get Arcane Blast Debuff you can cast Arcane blast 2.25 sec for the same amount of mana as the 3 sec cast if you manage to finish the spell after the debuff runs out -
( Debuff = mana increase of AB and it lasts 6 seconds )
So what i ussually do in raid, is AB (2.5 sec ) - Arcane missiles ( Which is 5 seconds channeling ) and then AB (2.17 sec) - arcane missiles - AB (2.5 sec ) and continue that cycle -
not sure this is an exploit or not but it might be usefull to some of you mages out there- Hope i was of help