GTS-T/GTR rotors are actually much cheaper than the Silvia/180 rotors, plus the silvia/180 rotors are too thin, they are 22mm (i think?) whereas for the 4 piston calipers, depending on the type of caliper (iron, aluminium, turbo, NA etc) are anywhere from 28mm to 32mm thick. the ones i am going to use require 30mm thick rotors (or could be 28mm, i can't remember).