I've talked to a KW engineer in Germany. The GTS uses custom valved dampers specified by M GmbH. As for springs they are supposedly "custom" as well, but "similar" to the CS kit.
Front rate is not yet confirmed, but length is 170 mm.
Rear rate is 140 N/mm (799#/in), length is unknown.
E92 M3 DCT - AiM EVO4 Data Logger / AiM SmartyCam HD / KW Competition 2-Way / OMP ARS Racing Seats / Brembo GT 365 / Pagid Yellow RS-29 / Rear Seats Delete