In terms of overall gaming performance, the graphical capabilities of the AMD Radeon HD 8870M are noticeably better than the AMD Radeon R9 M365X 4GB.

The Radeon HD 8870M has a 100 MHz higher core clock speed and the same number of Texture Mapping Units as the R9 M365X. This results in the Radeon HD 8870M providing 4 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 Radeon HD 8870M has a 100 MHz higher core clock speed than the R9 M365X and the same number of Render Output Units. This results in the Radeon HD 8870M providing 1.6 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 M365X was released over a year more recently than the Radeon HD 8870M, and so the R9 M365X is likely to have better driver support, meaning it will be more optimized for running the latest games when compared to the Radeon HD 8870M.

The R9 M365X has 2048 MB more video memory than the Radeon HD 8870M, so is likely to be much better at displaying game textures at higher resolutions. However, overall, the Radeon HD 8870M has superior memory performance.

The Radeon HD 8870M has 8 GB/sec greater memory bandwidth than the R9 M365X, which means that the memory performance of the Radeon HD 8870M is marginally better than the R9 M365X.

Both the Radeon R9 M365X 4GB and the Radeon HD 8870M have 640 Shader Processing Units. While the two GPUs have the same number of SPUs, the actual performance delivered by the Radeon HD 8870M is 496 and by the R9 M365X is 496. Knowing that the shader performance of the Radeon HD 8870M is superior, it is not necessary to examine the GPUs' respective Texture and Pixel Fill Rates.

The Radeon R9 M365X 4GB requires 50 Watts to run and the Radeon HD 8870M requires 50 Watts. The two GPUs require the same amount of wattage to run. As such, there is no need to worry about which will more significantly affect your yearly electricity bills.