I sell the C5 / C6 upgrade kit for the front on eBay here in Germany for many years now and I think there is no one who would step back to oem C4 ZR-1 front brake after installing this brakes. The main difference are the 50 % larger brake pads if you compare C5 / C6 with C4 ZR-1.
https://www.ebay.de/itm/334050662572...kAAOSwuhhXVYIj