In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GTX 780M SLI are massively better than the Nvidia GeForce 940MX 2GB.

The GeForce 940MX 2GB has a 351 MHz higher core clock speed than the GTX 780M, but the GTX 780M has 232 more Texture Mapping Units than the GeForce 940MX 2GB. As a result, the GTX 780M exhibits a 170.5 GTexel/s better Texture Fill Rate than the GeForce 940MX 2GB. This still holds weight but shader performance is generally more relevant, particularly since both of these GPUs support at least DirectX 10.

The GeForce 940MX 2GB has a 351 MHz higher core clock speed than the GTX 780M, but the GTX 780M has 56 more Render Output Units than the GeForce 940MX 2GB. As a result, the GTX 780M exhibits a 40.3 GPixel/s better Pixel Fill Rate than the GeForce 940MX 2GB. However, both GPUs support DirectX 9 or above, and pixeling performance is only really relevant when comparing older cards.

The GeForce 940MX 2GB was released over a year more recently than the GTX 780M, and so the GeForce 940MX 2GB is likely to have better driver support, meaning it will be more optimized for running the latest games when compared to the GTX 780M.

The GTX 780M has 6144 MB more video memory than the GeForce 940MX 2GB, so is likely to be much better at displaying game textures at higher resolutions. This is supported by the fact that the GTX 780M also has superior memory performance overall.

The GTX 780M has 304 GB/sec greater memory bandwidth than the GeForce 940MX 2GB, which means that the memory performance of the GTX 780M is massively better than the GeForce 940MX 2GB.

The GeForce 940MX 2GB has 384 Shader Processing Units and the GeForce GTX 780M SLI has 3072. However, the actual shader performance of the GeForce 940MX 2GB is 644 and the actual shader performance of the GTX 780M is 2448. The GTX 780M having 1804 better shader performance and an altogether better performance when taking into account other relevant data means that the GTX 780M delivers a massively smoother and more efficient experience when processing graphical data than the GeForce 940MX 2GB.

The GeForce 940MX 2GB requires 25 Watts to run and the GeForce GTX 780M SLI requires 200 Watts. The GTX 780M requires 175 Watts more than the GeForce 940MX 2GB to run. The difference is significant enough that the GTX 780M may have an adverse affect on your yearly electricity bills in comparison to the GeForce 940MX 2GB.