Today I went to Nikon service in Shinjuku, Tokyo where both D5 and D500 were on display. I played around with it. What I noticed was that the live view is noticeably improved over that of D4, the time lag is short enough to focus manually without being frustrated. The shutter responce was also noticeably better. The live view of D500 was also improved over D7200, but not as dramatically as on D5.
D5 was slightly larger than D4/4S (about 5mm taller and a few milimeters wider than D4/4S). D500 was roughly as large as D300.