In terms of overall gaming performance, the graphical capabilities of the Nvidia GeForce GTX 645 (OEM) are very slightly better than the AMD Radeon HD 7750 1GB GDDR5.
The GTX 645 has a 23 MHz higher core clock speed and 16 more Texture Mapping Units than the HD 7750. This results in the GTX 645 providing 13.9 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 645 has a 23 MHz higher core clock speed than the HD 7750 and the same number of Render Output Units. This results in the GTX 645 providing 0.4 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 GTX 645 was released over a year more recently than the HD 7750, and so the GTX 645 is likely to have better driver support, meaning it will be more optimized for running the latest games.
The GeForce GTX 645 (OEM) and the Radeon HD 7750 1GB GDDR5 have the same amount of video memory, but are likely to provide slightly different experiences when displaying game textures at high resolutions.
The HD 7750 has 8 GB/sec greater memory bandwidth than the GTX 645, which means that the memory performance of the HD 7750 is marginally better than the GTX 645.
The GeForce GTX 645 (OEM) has 576 Shader Processing Units and the Radeon HD 7750 1GB GDDR5 has 512. However, the actual shader performance of the GTX 645 is 511 and the actual shader performance of the HD 7750 is 348. The GTX 645 having 163 better shader performance and an altogether better performance when taking into account other relevant data means that the GTX 645 delivers a marginally smoother and more efficient experience when processing graphical data than the HD 7750.
The GeForce GTX 645 (OEM) requires 65 Watts to run and the Radeon HD 7750 1GB GDDR5 requires 55 Watts. We would recommend a PSU with at least 450 Watts for the GTX 645 and a PSU with at least 400 Watts for the HD 7750. The GTX 645 requires 10 Watts more than the HD 7750 to run. The difference is not significant enough for the GTX 645 to have a noticeably larger impact on your yearly electricity bills than the HD 7750.