The R9 280X has a 120 MHz higher core clock speed than the GTX 780, but the GTX 780 has 64 more Texture Mapping Units than the R9 280X. As a result, the GTX 780 exhibits a 47.4 GTexel/s better Texture Fill Rate than the R9 280X. This still holds weight but shader performance is generally more relevant, particularly since both of these GPUs support at least DirectX 10.
The R9 280X has a 120 MHz higher core clock speed than the GTX 780, but the GTX 780 has 16 more Render Output Units than the R9 280X. As a result, the GTX 780 exhibits a 11.8 GPixel/s better Pixel Fill Rate than the R9 280X. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.
The R9 280X was released less than a year after the GTX 780, 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 280X Sapphire Toxic 3GB OC Edition and the GeForce GTX 780 MSI Lightning Edition have the same amount of video memory, but are likely to provide slightly different experiences when displaying game textures at high resolutions.
The R9 280X has 18.8 GB/sec greater memory bandwidth than the GTX 780, which means that the memory performance of the R9 280X is slightly better than the GTX 780.
The Radeon R9 280X Sapphire Toxic 3GB OC Edition has 2048 Shader Processing Units and the GeForce GTX 780 MSI Lightning Edition has 2304. However, the actual shader performance of the R9 280X is 2120 and the actual shader performance of the GTX 780 is 2380. The GTX 780 having 260 better shader performance and an altogether better performance when taking into account other relevant data means that the GTX 780 delivers a noticeably smoother and more efficient experience when processing graphical data than the R9 280X.
The Radeon R9 280X Sapphire Toxic 3GB OC Edition requires 250 Watts to run but there is no entry for the GeForce GTX 780 MSI Lightning Edition. We would recommend a PSU with at least 600 Watts for the GTX 780, but we do not have a recommended PSU wattage for the R9 280X.