If you guys want to get an idea of wheel clearance when using C6 discs, I've attached 2 pdf brake profiles. One with C6 Z51 discs that are 340x32mm and one with C6 Z06 discs that are 355x32m.
These are 1:1 scale, so you can print them out at full size if you uncheck the "fit to page" option. The hatched rectangle on the bottom will fit into the wheel centerbore in order to properly locate the profile.
Using off-the-shelf OE parts ends up making for worse clearance than if a system was really designed specifically for the C4. The C4 disc is much deeper than the C6 or C7 cars, by almost 1/2".
