Yep different GPUs. Not directly comparable as shown before.
The last conclusion we can draw is that the AMD Radeon HD 7970 GHz edition suffers less from CPU scaling than the Nvidia GeForce GTX 680. That means that the AMD card performs better with slower processors compared to the Nvidia card. We don't have a clear explanation for this, but it's possible it has something to do with the driver overhead.
680 just likes intel CPUs more for some reason. 7970 plays nicely with both(maybe AMD driver optimization?). One more reason for AMD users to stick with AMD GPUs