In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GTX 680M SLI are massively better than the AMD Radeon HD 8850M.

The GTX 680M has a 95 MHz higher core clock speed and 184 more Texture Mapping Units than the Radeon HD 8850M. This results in the GTX 680M providing 136.3 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 680M has a 95 MHz higher core clock speed and 48 more Render Output Units than the Radeon HD 8850M. This results in the GTX 680M providing 36.1 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 HD 8850M was released less than a year after the GTX 680M, and so they are likely to have similar driver support for optimizing performance when running the latest games.

The GTX 680M has 2048 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 680M also has superior memory performance overall.

The GTX 680M has 198.4 GB/sec greater memory bandwidth than the Radeon HD 8850M, which means that the memory performance of the GTX 680M is massively better than the Radeon HD 8850M.

The Radeon HD 8850M has 640 Shader Processing Units and the GeForce GTX 680M SLI has 2688. However, the actual shader performance of the Radeon HD 8850M is 496 and the actual shader performance of the GTX 680M is 1935. The GTX 680M having 1439 better shader performance and an altogether better performance when taking into account other relevant data means that the GTX 680M 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 680M SLI requires 200 Watts. The GTX 680M requires 155 Watts more than the Radeon HD 8850M to run. The difference is significant enough that the GTX 680M may have an adverse affect on your yearly electricity bills in comparison to the Radeon HD 8850M.