First, the easiest call we can make is that the Radeon HD 6850 CrossFireX setup does indeed offer performance comparable to a single GeForce GTX 580 at a lower price. That combo adds up to a very nice value proposition, provided you are willing to sacrifice four expansion slots worth of space in your PC for graphic cards—and provided you're willing to live with the occasional compatibility and performance pitfalls one will inevitably encounter with a multi-GPU solution.
If you know for certain you want to drive a two-megapixel display and nothing more, a couple of GTX 460 768MB cards might not be a bad proposition. Even so, you may find your performance hindered by the smaller amount of video RAM at higher quality levels, as we did at 1920x1080 in Metro 2033.
The GTX 460 768MB works hard to keep the primary GPU's temperature relatively low, at 73°C, and that shows on the decibel meter, where only the GTX 460 1GB cards are louder. The 6850 CrossFireX pairing, meanwhile, maintains decent temperatures but registers substantially lower noise levels.
http://techreport.com/articles.x/20043/1
Single vs MultiGPU, Performance vs Price
2nd December 2010, 16:19
Single vs MultiGPU, Performance vs Price 
