ur system ram is way slower compared to ram on the g-card . i dunno abt the performance diff between 8400GS and GT . i didnt know that 8400GT existed , i thot only 8400GS was there . XFX uses higher quality components like capacitors , PCB , etc.. which are more stable and allow better OCing . thats y xfx , evga(not in india AFAIK ) , BFG ( not in india AFAIK ) are preferred .