Switch, One X and PS4 pro (and some older systems) are on a 55" Samsung 4k60hz/1440p120hz HDR1000 TV with freesync ultimate support
PC, One S and PS4 fat are on a 27" Dell PC Monitor, 1440p144hz (165hz overclockable)
the Samsung has 7 ms to 11ms lag (7ms on 120hz and 11ms on 60hz)
the Dell has 1 to 2 ms lag (low latency mode for 1ms)
I don't think I'm gonna upgrade soon, most games nextgen that will support 120fps will most likely barely reach 1440p with only a few exceptions, so I think HDMI2.0 still covers next gen well enough.