I'm 667 Item level, and i have no issues sustaining great raid dps on any fight. Some of it has to do with how long have you played this class, as well how are you doing the fights strat wise....
I also went Full mastery for enchants/gems. I feel its great for consistant dps rather than relying on your Crit chance.
I low seeing those +130,000 Chaos Bolts.