Thank you for replying. I understand the limitations. According to the nVidia Control Panel help file, G-Sync requires "NVIDIA GeForce GTX 650 Ti BOOST or higher GPU (or Kepler-class or later Quadro GPU)" That particular GPU was released in March 2013, whereas mine was released June 2012 but is still Kepler-class. I looked up the specs on Techpoweredup but couldn't see where to find the pixel clock. There are some differences on that page however as mine definitely has an output, the Mini-DisplayPort I am using. It also seems as if the 680M has better specs than the 650 Ti except for clock speeds, but as I am not extremely familiar with reading these specs perhaps I am missing something. Their 'relative performance' comparison list does show the 650 Ti Boost at 89% vs the 680m though.
As I say, I am using it at 60Hz non-overclocked do to the flickering problems I had. That isn't the current issue though it does somewhat ruin the purpose of buying this particular monitor in the first place. The issue is that it is crashing my computer, specifically it is causing a driver_irql_not_less_or_equal in one of the nVidia sys files: nvlddmkm.sys.