The GTX 980 has a 108 MHz higher core clock speed than the Radeon R9 295X2, but the Radeon R9 295X2 has 224 more Texture Mapping Units than the GTX 980. As a result, the Radeon R9 295X2 exhibits a 214.2 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 108 MHz higher core clock speed than the Radeon R9 295X2, but the Radeon R9 295X2 has 64 more Render Output Units than the GTX 980. As a result, the Radeon R9 295X2 exhibits a 58.2 GPixel/s better Pixel Fill Rate than the GTX 980. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.
The GTX 980 was released less than a year after the Radeon R9 295X2, 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 Radeon R9 295X2 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 Radeon R9 295X2 also has superior memory performance overall.
The Radeon R9 295X2 has 415.6 GB/sec greater memory bandwidth than the GTX 980, which means that the memory performance of the Radeon R9 295X2 is massively better than the GTX 980.
The GeForce GTX 980 MSI 4GB Edition has 2048 Shader Processing Units and the Radeon R9 295X2 has 5632. However, the actual shader performance of the GTX 980 is 3362 and the actual shader performance of the Radeon R9 295X2 is 5160. The Radeon R9 295X2 having 1798 better shader performance and an altogether better performance when taking into account other relevant data means that the Radeon R9 295X2 delivers a massively smoother and more efficient experience when processing graphical data than the GTX 980.
The GeForce GTX 980 MSI 4GB Edition requires 180 Watts to run and the Radeon R9 295X2 requires 500 Watts. We would recommend a PSU with at least 500 Watts for the GTX 980 and a PSU with at least 850 Watts for the Radeon R9 295X2. The Radeon R9 295X2 requires 320 Watts more than the GTX 980 to run. The difference is significant enough that the Radeon R9 295X2 may have an adverse affect on your yearly electricity bills in comparison to the GTX 980.