In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GTX 960M 4GB are very slightly better than the Nvidia GeForce GTX 950M 2GB.

The GTX 960M has a 115 MHz higher core clock speed and the same number of Texture Mapping Units as the GTX 950M. This results in the GTX 960M providing 4.6 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 GTX 960M has a 115 MHz higher core clock speed than the GTX 950M and the same number of Render Output Units. This results in the GTX 960M providing 1.9 GPixel/s better pixeling performance. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.

Both the GeForce GTX 960M 4GB and the GeForce GTX 950M 2GB were released at the same time, so are likely to be quite similar.

The GTX 960M has 2048 MB more video memory than the GTX 950M, so is likely to be much better at displaying game textures at higher resolutions. This is supported by the fact that the GTX 960M also has superior memory performance overall.

The GTX 960M has 0.2 GB/sec greater memory bandwidth than the GTX 950M, which means that the memory performance of the GTX 960M is marginally better than the GTX 950M.

Both the GeForce GTX 960M 4GB and the GeForce GTX 950M 2GB have 640 Shader Processing Units. While the two GPUs have the same number of SPUs, the actual performance delivered by the GTX 960M is 948 and by the GTX 950M is 858. Knowing that the shader performance of the GTX 960M is superior, it is not necessary to examine the GPUs' respective Texture and Pixel Fill Rates.

The GeForce GTX 960M 4GB requires 50 Watts to run and the GeForce GTX 950M 2GB 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.