Having had chance to consider the
features offered by both cameras, I believe the D500 is the better
choice to sit alongside an existing D4S. The marginal increase in
resolution offered by the D5 won't offer any real world advantage
over the D4S and the current flagship has high ISO capability
aplenty. Looking at the D500 there's a great deal to like: A smaller,
lighter body for occasions where minimal gear is appropriate, no
anti-aliasing filter for sharper images from the camera and a tilt
screen for video. Add to that, the D500 is the better connected
camera. Looking at the existing Nikon lens line up, the 14-24mm is a
superb lens, but focal lengths wider than 20mm have limited use. On
the D500 it becomes an altogether more useful 21-36mm with the
benefit of more depth of field as a result of the DX format. At the
other end, the 70-200mm II which is marginally less useful than it
might otherwise be due to considerable breathing would get a valuable
boost. The 24-70, while a good lens, is not quite as capable as the
other two key zooms usually carried and could be left behind, leaving
coverage from 14-300mm (or so) depending on which lens is mounted on
which body at the more useful focal lengths.