I wouldn't call a 6k monitor "nice", that's way above that. I would love on of those, since I can't stand blurry text, but even for me that's way too expensive to justify. So as the sibling says, if people are looking at old used pcs on ebay, they're unlikely to drop more than a grand on the screen.
A 32" 4k screen is nice enough and a reasonable one [0] can be had for a third of that. My I don't-know-how-old desktop I saved from the bin at work sporting an i5-6500 could drive that with no issues.
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[0] Around 2020 I bought an LG something-or-other for 350 Euros for work, 32", 4k, some form of VA panel. It had pretty good colors and better contrast than the IPS monitor I use as a Sunday-photographer.
A 32" 4k screen is nice enough and a reasonable one [0] can be had for a third of that. My I don't-know-how-old desktop I saved from the bin at work sporting an i5-6500 could drive that with no issues.
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[0] Around 2020 I bought an LG something-or-other for 350 Euros for work, 32", 4k, some form of VA panel. It had pretty good colors and better contrast than the IPS monitor I use as a Sunday-photographer.