CP5575's are current models. They were developed for a type of wheel used on an M3, BG had lots to do with that I believe as they work directly with AP. I'm not sure but if you went to Demon Tweeks or a retailer like that you may not even have them available. Who's providing these for you? If you ring AP directly they'll give you a price for the kit but you'll have to buy through an outlet for them such as BG. AP technical know BG (David Fuller is a key contact for them) and have worked closely with them. Buying through them will give you access to first class tech support.
Rears to match with an AP rotor and bell will probably cost you around £800 at a guess, maybe more. I toyed with the idea but a standard S3 setup with the right pads and fluid is more than up to the job. I use mine on track but if I didn't I'd say this spec is way over the top. I have currently an S3 f/r setup and it is/was fine for the road. Never had any issues at all.