I've asked this question before myself. I have an NVidia Optimus setup (680M & HD4000), and although the NC client insists its using the Intel, Optimus does actually do its job and switch over to the NVidia when in game.
Run MSI Afterburner and you'll see the NVidia is being used. It is for me anyway.
Also, a note: You cannot disable Optimus. It is simply not possible.