I'd expect the front to be more effective in slowing the bike down, but the rear to lock up the rear tire quicker. The rear will not stop the bike as quickly though it will lock up fast. The front will not lock up as fast but will and should stop the bike far more effectively than just using the rear. I run a 200mm in front and a 160 at the back. The front always slows the bike down a lot more quickly. For me, a bigger-than-160mm rotor in the back would just be overkill with no benefit.