Personally, I would wait. The next generation of GPUs is right around the corner, maybe even toward the end of this month. The Maxwell technology that Nvidia is using in the GTX 750 will be implemented in the next gen GPUs. We still dont even have a release date yet for Star Citizen, so why would you rush out and buy new components which could very well be outdated by the time the game is released. So it makes sense to wait for the next gen of GPUs. Even if you dont get an 800 series the 780s and the like will be reduced in price. As far as NVIDIA vs ATI it would still pay to wait and see what changes DX11 makes to the API. With Star Citizen supporting Mantel it seems that ATI would be the GPU of choice for the time being. So just wait for a while, unless you absolutely have to have something now, I would suggest the R9 290 over the GTX 780 just because of the Mantel support.