In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GTX 980 4GB are very slightly better than the AMD Radeon R9 390X PowerColor Devil 8GB Edition.

The GTX 980 has a 26 MHz higher core clock speed than the R9 390X, but the R9 390X has 48 more Texture Mapping Units than the GTX 980. As a result, the R9 390X exhibits a 49.5 GTexel/s better Texture Fill Rate than the GTX 980. This still holds weight but shader performance is generally more relevant, particularly since both of these GPUs support at least DirectX 10.

The GTX 980 has a 26 MHz higher core clock speed than the R9 390X and the same number of Render Output Units. This results in the GTX 980 providing 1.7 GPixel/s better pixeling performance. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.

The R9 390X was released less than a year after the GTX 980, and so they are likely to have similar driver support for optimizing performance when running the latest games.

Both GPUs exhibit very powerful performance, so it probably isn't worth upgrading from one to the other, as both are capable of running even the most demanding games at the highest settings.

The R9 390X has 4096 MB more video memory than the GTX 980, so is likely to be much better at displaying game textures at higher resolutions. This is supported by the fact that the R9 390X also has superior memory performance overall.

The R9 390X has 166 GB/sec greater memory bandwidth than the GTX 980, which means that the memory performance of the R9 390X is massively better than the GTX 980.

The Radeon R9 390X PowerColor Devil 8GB Edition has 2816 Shader Processing Units and the GeForce GTX 980 4GB has 2048. However, the actual shader performance of the R9 390X is 2633 and the actual shader performance of the GTX 980 is 3362. The GTX 980 having 729 better shader performance is not particularly notable, as altogether the R9 390X performs better when taking into account other relevant data.

The Radeon R9 390X PowerColor Devil 8GB Edition requires 275 Watts to run and the GeForce GTX 980 4GB requires 165 Watts. We would recommend a PSU with at least 750 Watts for the R9 390X and a PSU with at least 500 Watts for the GTX 980. The R9 390X requires 110 Watts more than the GTX 980 to run. The difference is significant enough that the R9 390X may have an adverse affect on your yearly electricity bills in comparison to the GTX 980.