your better off using XR4i disc's(253mm) and then either XR4i or cossie 2wd calipers(their the same thing)! with this set up you wont get a hint of the rears overpowering the fronts and the car swapping ends!!
Dont use cossie 4x4 vented disc's and calipers or it will want to swap end's under heavy braking!!