I would say that you do not need a BBK for Auto cross. Upgrade your pads and rotors, and change out your fluid...
ATE Super Blue DOT 4 Fluid
No need for added unsprung weight just to stop... Your ABS will take care of that for you. All the big brake kits will do is fight with ABS to do their jobs, and you end up wasting money for performance that you don't get.
Either remove the ABS and go with a race set up, or make your street setup incredible...