Thanks for help. As I've been playing hackintosh for quite a long time, I know a little bit about the graphic switching technic of Macs. It seems that the graphic card of 15" MBPR (discrete graphic models) can't be switch on the internal screen under Windows either. The Mac's graphic card switching technic depends on a hardware call GMUX. Only if we know how to access the hardware, will we able to switch graphic card of the internal screen of 15" MBPR (with discrete graphic models) under Windows. Have you tried mirroring the external screen to internal screen or using the app, gfxCardStatus, to switch graphic card under OSX? Maybe it will magically works with help of this app... Btw, do you think GTX660 or GTX750Ti is good enough to play BF4 or Crysis3 with the retina screen?