#1. Just like the Crichton Leprechaun, there is no such thing as a “400Z.”
B. Asking about a brake upgrade is like asking “which car should I buy?” the only correct answer is “anything but a Mustang,” but with brakes you have a lot of good options for upgrading all four corners for sub-$2K to $10K+.
My opinion, without spending craptons on it:
If I had a Sport, 19” wheels, and was looking, I’d consider the front NISMO (Akebono) conversion. Very similar to a Brembo kit (15”) only the NISMO/Akebono is a 4-pot vs the Brembo 6-pot calipers. But it’s 1/2 to 1/3 the cost of a Brembo front kit. To complete this you could go OEM perf/NISMO Akebonos on the rear. Whole thing probably $2,500.
You could also go with the Perf 355mm front setup. A little cheaper than the OEM 15” and many more pad and rotor options.
Lots of options for you. Just go with a known brand, not some Alibaba knockoff garbage. Brakes aren’t something to gamble with.
Factory akebono brakes come with 14 inch rotors already which are massive and more than enough for street driving
The real question is, what do you need from your brakes?
Tires have alot do with with braking ability as well
If your car a street car, you don't need anything but to replace the tires, pads, and rotors when worn
If you just want something for the parking lot....i guess powdercoated calipers?
If you are a show car, . . .. whatever big brake kit maker will sponsor you
If you actually need braking performance, track folks are constantly looking for more cooling as the weight of the RZ34 puts a heavy tax on all the components.
Those real upgrades involve brake ducting, better pads, 2 piece rotors, and better fluid. Above stock power levels, we're into AP Racing full replacement territory