The Bottom Line
Based on our evaluations here, the Radeon HD 6990 CrossFireX solution is looking like the more value oriented setup compared to GeForce GTX 590 SLI. There are many good things going for CrossFireX Quad, you have more RAM per GPU which translates into real-world gameplay improvements, the power consumption is a bit lower, availability is a bit better, and pricing isn't as harsh. We also like the ease and simple nature of AMD Eyefinity setup. When you add all of this up, Radeon HD 6990 CrossFireX is a better value.
The way things are, GeForce GTX 590 is better suited for lower resolutions, which is odd to say, but true according to our testing. When the video card is not memory bottlenecked at lower resolutions, GTX 590 SLI performs very well, though 6990 CFX is a slight step ahead each time, it is still competitive at lower resolutions. But if you want to go for that high resolution display setup, only the Radeon HD 6990 CrossFireX will provide that Quad-GPU experience you are looking for.
Still, expect issues when it comes to gaming as neither AMD nor NVIDIA have done the proper real world testing to support these configurations the way these should be supported. And the resonating fact of the matter is that 4-GPU SLI or CrossFireX scaling always seems to fall a bit flat. We would suggest that most of our readers would be best off with a 3-GPU configuration at the most and 2-GPU solutions show the best performance scaling.
