In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GTX 660M are very slightly better than the AMD Radeon HD 8850M.

The GeForce GTX 660M has a 210 MHz higher core clock speed but 8 fewer Texture Mapping Units than the Radeon HD 8850M. The lower TMU count doesn't matter, though, as altogether the GeForce GTX 660M manages to provide 1.7 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 GeForce GTX 660M has a 210 MHz higher core clock speed than the Radeon HD 8850M and the same number of Render Output Units. This results in the GeForce GTX 660M providing 3.4 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 over a year more recently than the GeForce GTX 660M, and so the Radeon HD 8850M is likely to have better driver support, meaning it will be more optimized for running the latest games when compared to the GeForce GTX 660M.

The Radeon HD 8850M and the GeForce GTX 660M have the same amount of video memory, but are likely to provide slightly different experiences when displaying game textures at high resolutions.

The GeForce GTX 660M has 32 GB/sec greater memory bandwidth than the Radeon HD 8850M, which means that the memory performance of the GeForce GTX 660M is noticeably better than the Radeon HD 8850M.

The Radeon HD 8850M has 640 Shader Processing Units and the GeForce GTX 660M has 384. However, the actual shader performance of the Radeon HD 8850M is 496 and the actual shader performance of the GeForce GTX 660M is 365. The Radeon HD 8850M having 131 better shader performance is not particularly notable, as altogether the GeForce GTX 660M performs better when taking into account other relevant data.

The Radeon HD 8850M requires 45 Watts to run and the GeForce GTX 660M requires 50 Watts. The GeForce GTX 660M requires 5 Watts more than the Radeon HD 8850M to run. The difference is not significant enough for the GeForce GTX 660M to have a noticeably larger impact on your yearly electricity bills than the Radeon HD 8850M.