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.
2011 E92 M3 DCT
1991 Spec Miata
2008 E92 M3 DCT
2008 E92 M3 6MT
2008 E92 335xi