As Luke said use GTR stuff as that's what GTS4's come with from factory. Putt GTST and GTS4 springs side by side and the GTS4 springs are much thicker.
Had R888's on my 32 and once warm could hold 2nd gear traction in RWD with 320kw's and they where 245/18's. They also lasted about 4-5 mallala track days.