I have done a bunch of research on monitors in this size class. Unfortunately the available options in this size / resolution class are not very good.
The two monitors you posted are not great options, for a number of reasons.
Right now, your only decent option is the Dell P4317Q. Looks like there is a used one on Amazon for around $750. The next model down, the Wasabit Mango UHD430, has enormous input lag. Both of these panels also have a BGR subpixel layout, which is non-ideal for OS’s other than Windows and also some programs as well (I think Google Chrome may be one, can’t recall right now).
There were a few okay models using VA panels around 40", but those appear to all be gone now.
The only large monitor that I can really sign off on right now is the XR382CQK, but it is very expensive. There are a few other models that use this same panel too but they aren’t cheaper.
If you’re willing to go down to 32" 4k, the BL3201PH can be had for $670 on eBay and is a great model.
LMK if you have any questions about this.