With a lot of experience with locating and trying to develop upgrade kits for the RCZ, it must be known that yes there are two brake systems on the RCZ and they are not interchangeable (fronts only, rears are all the same on the RCZ and RCZ 'R'):
Standard = 302mm
Sport = 340mm
R = 380mm
Sport brakes came standard on some RCZ's but were an option on others. So you could find a THP156 with Sport brakes, but this didn't happen often. If you got Sport brakes with your RCZ, Peugeot required that you also get 19" wheels, but to be honest you can fit an 18" wheel as well.
The mounting of the Standard caliper is not the same as the Sport caliper due to the disc diameter difference and you cannot bolt on Sport brakes on the Standard setup without new brackets, which you get with upgrade kits.
The Tarox system that we sell is designed to be used for Standard brake upgrades:
http://shop.rczperformance.com/product.sc?productId=162&categoryId=99
We do offer the Brembo although we are in the middle of pricing it correctly again for this year, but this is designed around upgrading a Sport brake system.
We see no real reason to upgrade the rear brakes and this also brings in another thing to consider and that is brake balance. Too large a disc on either front or rear will require brake balancing and this is not so straight-forward with the RCZ. 365mm is the maximum for the front without having to balance it with the rear. The next step up is to 380 but then yes balance is required, as in the 'R', unless you do increase the size of the rear discs.
Unfortunately with the RCZ not being produced for much longer and the numbers of them not being astronomically high, brake manufacturers are not really interested in developing systems for them especially if you have the Sport brakes already.
We had an experimental system on ours but eventually removed them as we were not happy with the design, quality, and performance. When we went back to the Sport brakes we were very happy with the performance, yes the Sport brakes are very very good.
At the end of the day these are your brakes and is not something you should go cheap on if you are looking at upgrading them is size.
Contact us if you have any other questions regarding brakes.