In terms of overall gaming performance, the graphical capabilities of the AMD Radeon HD 7970M Crossfire are massively better than the AMD Radeon HD 8850M.

The HD 7970M has a 225 MHz higher core clock speed and 120 more Texture Mapping Units than the Radeon HD 8850M. This results in the HD 7970M providing 111 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 HD 7970M has a 225 MHz higher core clock speed and 48 more Render Output Units than the Radeon HD 8850M. This results in the HD 7970M providing 44.4 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 less than a year after the HD 7970M, and so they are likely to have similar driver support for optimizing performance when running the latest games.

The HD 7970M 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 HD 7970M also has superior memory performance overall.

The HD 7970M has 275.2 GB/sec greater memory bandwidth than the Radeon HD 8850M, which means that the memory performance of the HD 7970M is massively better than the Radeon HD 8850M.

The Radeon HD 8850M has 640 Shader Processing Units and the Radeon HD 7970M Crossfire has 2560. However, the actual shader performance of the Radeon HD 8850M is 496 and the actual shader performance of the HD 7970M is 1850. The HD 7970M having 1354 better shader performance and an altogether better performance when taking into account other relevant data means that the HD 7970M 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 Radeon HD 7970M Crossfire requires 200 Watts. The HD 7970M requires 155 Watts more than the Radeon HD 8850M to run. The difference is significant enough that the HD 7970M may have an adverse affect on your yearly electricity bills in comparison to the Radeon HD 8850M.