The front brake system on all KX500's is less than steller. However, there are several big brake systems out there that will improve the front stopping power. It will set you bake about $150, but worth the money. As for brake pads, I refuse to use anything but stock. I have been given pads on many occassions to "test", and ALWAYS go back to the stock pads. Yes, they are more expensive. Yes, they are hard on rotors. Yes, they stop better. The only other pad I will use in a pinch are the stock pads from a CR250 (yup, they fit just fine). My only complaint is that they are noisier than the KX pads, so I only use long enough to get me though the race or ride until I can get the stock Kawasaki's.
Rick