4K video on 4.5K display?

[SazerLite]

I'm interested in getting an M4 iMac, and I'm positive the 24-inch 4.5K display will serve my purposes well.
But one question I have is how does a 4K video look on that display in fullscreen? Won't the visuals not look quite as good if the video's smaller resolution is being stretched out to fit on the monitor's higher resolution?

 

[HobeSoundDarryl]

You'll probably not be able to notice... like watching any live television (1080p or less) or even DVD quality (540p or less) on a 4K TV screen. High resolution video scales up pretty nicely (especially when so little scaling will be needed in this case) and scales down perfectly. This is not something with which to be overly concerned. If you need more than some strangers opinion, take a Mac to a monitor shop and connect it to 4K, 6K and 8K monitors. It will look pretty good on all of them.