Although I think the stock sport package brakes are going to be hard to beat, central 20 is offering a 6 piston caliper two piece rotor brake upgrade.
The front rotors are 370mm and the rear are 355, pretty damn big. The rear brakes are pretty neat, considering the Z has a intergal drum in the rear rotors for the parking brake, Central 20 still was able to do a two pice rotor for the rear, 4 piston caliper as well!
Personaly I think stock sport package brakes with two piece rotor, good pads and stainless lines will serve the purpose all the way up to actual racing, this kit is cool.
I hope things like compatabilty with the ABS and EDFC system was considered. Often big brake kits increse stopping distances in modern cars for these reasons.