The Nikon D5 and its predecessors are mainly intended for action and sports photographers. They are designed for speed and sensitivity in order to freeze fast moving action and capture it at its height.

This is the main reason why these models traditionally offer fewer megapixels. This lets the camera shoot faster, have better throughput and fit more images in its buffer. The D5 for example has a 20 MP sensor which can capture images at 14 FPS with the mirror locked up or 12 FPS normally for up to 200 JPEG or 170 RAW files.

Dynamic-range used to be better in the Dx series but I found the D5 does not quite match the D610 or even the D4S before it. However once ISO is raised, which is often the case for action photography, the D5 delivers better dynamic range than most full-frame DSLRs.

News and sports photography are events where time to publication is crucial, so these cameras offer many features to speed delivery. They have Ethernet ports, built FTP servers and a huge battery. The D5, for example, can capture 3780 image on a sinlge charge, which makes it less likely to miss a shot while changing batteries.

If you want all the details, you can read my detailed review of the Nikon D5 XQD, just published this week, or my review of the Nikon D4S. There are differences in performance between both models which means that the D4S still has an edge in some areas and conversely.