Willhub seems to think that upping the res will make gains smaller.
This is not the case.
Hence why they use that low res in the testing.
Willhub is right, the reason reviewers test CPU's at low resolutions is because this is where you see biggest difference, this is where your typically CPU limited with high end graphics cards, however when you increase the resolution and also enable settings like AA/AF the bottleneck mores over the GPU and the benefit from a faster CPU in this situation will be greatly reduced or even nullified.