no it will not and I believe you cannot add it to work anyways. you need similar specs and same architecture or so. if that's the case, then it will always take form of the lower gpu spec, and one more gpu will just increase compute performance, not in games. so don't do it unless you want to change in NVidia control panel to use the 640 as a PhysX card, but it will be NO use whatsoever to gaming while paired with a 960, possible even lower performance if it even works