That's an interesting comparison. The results tend to confirm the accuracy and relevance of DXOMark tests. If one compares the graphs for the D800 with the IQ180, in screen mode, one is comparing pixel quality, as you are attempting to do with the two crops of images taken with the same lens at the same focal length.
Despite the IQ180 pixel being marginally larger than the D800 pixel (5.17 microns as opposed to 4.7 microns), the quality of the D800 pixel is as 'close as matters' in respect of SNR at 18%, Tonal Range and Color Sensitivity.
For example, the Color Sensitivity of the D800 pixel is described as being 22 bits. That of the IQ180 is 21.5 bits. In other words, the Color Sensitivity of the D800 is actually better by 0.5 bits. However, DXO state that a difference of less than 1 bit would likely not be noticeable. The values for Tonal Range and SNR at 18% are even closer.
But there's one glaring difference, and that's DR. The DR of the D800 pixel is claimed by DXO to be 1.34 EV better than the IQ180 pixel. That is a difference that should be clearly noticeable in a very high contrast scene.
If I have one criticism of your comparison, it would be that you haven't chosen a scene with some significant areas of deep shadow containing detail, so we could see if the D800 pixel really does have noticeably better DR.
PS. The EXIF data is a bit puzzling. The IQ180 appears to have been shot at ISO 35 and 1/8th sec exposure. No mention of F stop. The D800E shot is at ISO 100, F2.8 and 1/500th
sec exposure. What's going on here? Why the huge difference in exposure?