Onur,

I emailed my P source and you are partially right. 

Yes, ceramic rotors from SGL use harder surface component but, this is very thin layer and as a consequence Porsche officially do not recommend PCCBs for track use apart from occasional track drive (few laps every few months).

Reason is that during heavy track driving PCCBs experince extremly high temperature amd since hard layer is very thin brakes are prone to extensive wear. Ask any GT3 owner why most (95%) of them use only steel brakes for track driving. 

Even better ask directly Porsche what are they reccomending for GT3 if you plan to drive extensivly on the track. PCCBs wont be their answer...