What is required or desirable in a 4K TV for a 4K gaming experience to be good (i.e., smooth video and transitions, no or minimal ghosting, low lag, fast refresh and so on)?

With the weekly announcements about FM7 my interest in racing in the console world has been piqued, again. I decided to check the prices of 4K TVs, and found that the prices for small ones start at a reasonably low level (about CAD500.00 for a 43" unit). Then I checked the prices of XBox consoles, and found that there is a new XBox coming soon, the XBox One X (the pre-order price for the special edition Scorpio unit was CAD600.00 but is sold out), which I understand is the first XBox to offer 4K gaming.