mine is ok. But have turned on the "game mode"
Can feel a bit sluggish when game mode is turn off.
Make sure you check the tv input lag before buying one.

It depends more on the TV than the system or your settings. If the TV has input lag at 4K, then no matter if you're running upscale or native there will be lag. Though there are arguments that upscaling is a process that should cause lag. So far it is not as noticeable as a 4KTV with poor 4K support in the first place. 1080p@60Hz and 4K@60Hz for most TVs are the same in terms of input lag. But once you turn off game mode, lag goes up.
Statistics here on how TVs handle input lag. (Lower numbers are better)
Note: I'm sure there are others with more experience out there, but this is for a perceived/noticeable difference. I'm sure we can argue 5-10% difference, but unless you are doing frame perfect speedruns, Mike Tyson's Punch-Out or still playing Rock Band. Most games are designed to take into account the lag found in HDTVs. So if you want a pure, lag-free gameplay. Going back to CRTs might be the solution.

30 ms is quite good.

I think it's good that you're passionate about it, it's the same reason why I don't say the Pro is a must-buy because there's just so many ifs, ands or buts to get it to work at it's optimal "best" performance. If I wanted to mess with the settings and go through pages and pages of research to get the optimum performance, I would just get a PC. But the point of a console is not to be asking does this work with this or does this work with that. Plug and play, enuff said.