See www.dxomark.com. The D4 result is not as controversial as the D800, but it is still good to see that the D4 is an improvement overall on the D3x, maybe even the D3s under the DxO test conditions.
But I really want to talk about the D800 results, where the D800 is now ranked 1st overall, ahead of the MF sensors. First, one has to keep in mind that DxO scales all the images to 8 MP when performing sensor tests, in other words, they are comparing relative image quality with a fixed print size in mind (roughly 12x8").
This means that the D800 images are scaled down quite a bit (about 4 pixels to 1), which increases the effective dynamic range, and reduces apparent noise. The bottom line is that the dynamic range scores of DxO mark usually favour higher resolution sensors, which is why the D3x used to be the FF champ.
Anyhow, if you choose a fixed print size IQ as your objective, the D800 really puts up a good show.
Looking at full size images (or much larger prints), the D800 will still have excellent dynamic range, i.e., it looks like this is the landscape FF body of choice.
And with that, let the nit-picking begin!