Tested FastSync and RTSS at 1fps and at least in DX9 ganes loose 1 frame of input lag. This is easily visible, after frame I would move mouse and game would have certain frames of delay before input would be registered. DX9 games on UE3 would behave this way as some other DX9 games and games forced in DX9. In DX11 I tested Tomb Raider and Ryse and no change was observed. More testing is needed. There was however no added input lag from FastSync even in these games. OpenGL games do not seem to support FastSync at all.