A:Answer The Xbox One S doesn't play native 4K games, that said it does a great job of up upscaling to 4K.
The quality of the images on the X940D is excellent, much better than I expected given what it looked like on my Vizio M70.
According to reviews the lag on the Sony in Game mode is about 20ms, a few milliseconds slower than the Vizio, but I can't notice any lag. Keep in mind that 20-25 ms is much shorter time than it takes for your eye to capture the light from the TV, send it to the brain, process the image, formulate a command, send it to the hands and fingers, and move your fingers.
You probably wouldn't notice lag until it was around 100ms, which is how long an eye blink lasts.
All in all playing Battlefield 1 or Forza on this Sony is a great experience.