A rebuild kit will return 100% of the capability. Im not aware of a bolt-on Brembo caliper. However the two piston caliper from an S2 FZ6 will bolt on and will a provide marginal performance improvement.
Upgraded OEM brakes as I noted above are adequate for typical aggressive street riding and even occasional track days. If you haven’t upgraded the forks, aggressive brakes will only amplify the inherent brake dive, and in my opinion would potentially create an unsafe condition.