[Mr GSR]

If you can lock up your brake (or cause ABS to come on, if you have it), then your brakes are good enough. Are pad with more "bite" will just cause this to happen sooner.
The best thing to upgrade would be your tires, since they are the most important aspect to braking fast. If you have grippy tires, you make the amount of force needed to break the tires loose higher, thus increasing your capability to brake fast. It all comes down to friction, an object sliding has a lower friction coefficent than and object not sliding, meaning the object sliding will not brake as fast. It's hard to push a box along the floor when it is sitting still, but get that box moving and it is much easier to push around, same idea with tires/brakes.