I'm not so sure 120Hz tfts will make any difference if you want to play with Vsync off, you are bound to still get tearing and I bet it will be just as annoying as tearing on 60Hz screens now. As you say it will only be useful if you can play at full res at 120fps all the time and therefore have vsync on, but since your graphics struggles to give 60 now I doubt you'll get any benefit from a 120Hz tft.