In terms of overall gaming performance, the graphical capabilities of the AMD Radeon R9 280 are marginally better than the AMD Radeon HD 7950 Gigabyte WindForce Edition.
The HD 7950 has a 33 MHz higher core clock speed and the same number of Texture Mapping Units as the Radeon R9 280. This results in the HD 7950 providing 3.7 GTexel/s better texturing performance. This still holds weight but shader performance is generally more relevant, particularly since both of these GPUs support at least DirectX 10.
The HD 7950 has a 33 MHz higher core clock speed than the Radeon R9 280 and the same number of Render Output Units. This results in the HD 7950 providing 1 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 Radeon R9 280 was released over a year more recently than the HD 7950, and so the Radeon R9 280 is likely to have better driver support, meaning it will be more optimized for 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 280 and the Radeon HD 7950 Gigabyte WindForce Edition have the same amount of video memory, but are likely to provide slightly different experiences when displaying game textures at high resolutions.
The memory bandwidth of the Radeon R9 280 and the Radeon HD 7950 Gigabyte WindForce Edition are the same, which means the Radeon R9 280 and the HD 7950 have equal limitations when it comes to graphical data transfer.
Both the Radeon R9 280 and the Radeon HD 7950 Gigabyte WindForce Edition have 1792 Shader Processing Units. The two GPUs are based on different architectures, but deliver an equivalent shader performance. To compare, we must continue to look at the memory bandwidth, Texture and Pixel Rates. In this case, the HD 7950 has 3.7 GTexel/s better Texture Fill Rate and 1 GPixel/s better Pixel Fill Rate, but the has GB/sec greater memory bandwidth. Although the GPUs are very similar in performance, the HD 7950 takes the edge.
The Radeon R9 280 requires 200 Watts to run but there is no entry for the Radeon HD 7950 Gigabyte WindForce Edition. We would recommend a PSU with at least 500 Watts for the Radeon R9 280.