17Z's are Brembo Calipers from a Touareg (I believe). They bolt on, but you have to use spacers in the bolts. You use Mercedes ML something rotors, which are around 330mm, and you need centering rings for the rotors as the center bore is different. Braking is apparently very powerful with this setup, but the ML rotors weigh a ton, almost equal to what R rotors weigh. Also the 17Z piston areas do not match the master cylinder very well.
The 18Z is basically the same as above (come off a Cayenne I believe), but uses 350mm rotors off another Mercedes.
The NQSBBK uses Brembo calipers from a Non-S Porsche Boxster 986, and utilizes stock 312mm rotors. You save 3-4 pounds per side from the lighter caliper, and the stock rotors are actually pretty light because they aren't HUGE one piece rotors. You run adapters from the caliper to the stock mounting holes, and can use stock brake lines with a different banjo bolt. Out of all the Porsche retrofits, these are the only ones that have piston diameters that perfectly match the master cylinder.
Shameless plug, I have a NQSBBK for sale: http://golfmk6.com/forums/showthread.php?t=78691
Stoptech kits use a two piece rotor which makes them lighter. Adapters are used to bolt up.
Specifed brembo kits also use two piece rotors for the most part, but I believe they do make a solid rotor for one of their kits. Adapters are used to bolt up.
Honestly, and I'm not just saying this because I'm selling a set, I like the NQSBBK the best. The stock size rotors are cheap and pretty light. The calipers save weight and are 4 piston. Pads are cheap. Master cylinder and piston areas match perfect. You can run 17's and even some 16's. No more floating caliper (you can say this for all of them). And it's the cheapest out of the bunch. There are only a handful of people that need huge BBK's that track every weekend. For everyone else, the NQSBBK seems perfect. I never even got to bolt mine on as I'm now selling them and trying to buy a beater vehicle I've been looking at for a while, but if they don't sell in a month you will see some pics of the boxster brembos behind some V710's!
