Brakes stop your wheel from turning, But it is the tyre connection to the ground which is as important. Changing your brakes to more powerful calipers with out any consideration to your tyres is a waste of time. I am a bit heavier than most at 112 kg and i find even deore brakes with 7 inch rotors that i have on one of my bikes can easily exceed the grip of the 2.25 highrollers on it, even in the best conditions. Modulation and predictability of knowing how hard you can push your tyres before they slip is more important than sheer power of the brakes.