If you are using a 1080p monitor or perhaps even outputting to a large 1080p TV, there is no point in picking up a $500+ GPU as you will not be using the majority of its capabilities.  Phoronix has just done research on what GPU offers you the best value for gaming at that resolution, putting five AMD GPUs from the Radeon R9 270X to the R9 Fury and six NVIDIA cards ranging from the GTX 950 to a GTX TITAN X into their test bench.  The TITAN X is a bit of overkill, unless somehow your display is capable of 200+ fps.  When you look at frames per second per dollar the GTX 950 came out on top, providing playable frame rates at a very low cost.  These results may change as AMD's Linux driver improves but for now NVIDIA is the way to go for those who game on Linux.

"Earlier this week I posted a graphics card comparison using the open-source drivers and looking at the best value and power efficiency. In today's article is a larger range of AMD Radeon and NVIDIA GeForce graphics cards being tested under a variety of modern Linux OpenGL games/demos while using the proprietary AMD/NVIDIA Linux graphics drivers to see how not only the raw performance compares but also the performance-per-Watt, overall power consumption, and performance-per-dollar metrics."

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Graphics Cards