CoC Spark, Cast Speed or Crit Bonus?

As title says, crafting a new BiS amulet, I'm at the end of my build and trying to squeeze out some more damage. Currently sitting at 769% crit bonus and 4.07 casts per second. Am I wrong to think that cast speed has no real effective dps gain at this point since i can machine gun it already and am limited in pure cast amounts in a short time as a blood mage?