the diameter of the point at which the force is applied due to better leverage. So, they will be 324/280 as good as stock (around an extra 15% braking power). Then there are also the fact that for each rotation the pad comes in contact with more metal (greater area) and they will be able to handle heat better due to increased mass.
Ginn or anyone else, is it necessary to machine the pad or caliper to get the bigger disk to fit?