In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GTX 780M SLI are massively better than the AMD Radeon HD 8850M.

The GTX 780M has a 146 MHz higher core clock speed and 216 more Texture Mapping Units than the Radeon HD 8850M. This results in the GTX 780M providing 172.4 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 GTX 780M has a 146 MHz higher core clock speed and 48 more Render Output Units than the Radeon HD 8850M. This results in the GTX 780M providing 39.3 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 GTX 780M was released less than a year after the Radeon HD 8850M, and so they are likely to have similar driver support for optimizing performance when running the latest games.

The GTX 780M has 6144 MB more video memory than the Radeon HD 8850M, 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 288 GB/sec greater memory bandwidth than the Radeon HD 8850M, which means that the memory performance of the GTX 780M is massively better than the Radeon HD 8850M.

The Radeon HD 8850M has 640 Shader Processing Units and the GeForce GTX 780M SLI has 3072. However, the actual shader performance of the Radeon HD 8850M is 496 and the actual shader performance of the GTX 780M is 2448. The GTX 780M having 1952 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 Radeon HD 8850M.

The Radeon HD 8850M requires 45 Watts to run and the GeForce GTX 780M SLI requires 200 Watts. The GTX 780M requires 155 Watts more than the Radeon HD 8850M 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 Radeon HD 8850M.