I use a multimonitor setup so unfortunately changing resolution isn't really an option since it'll mess up the layouts of my other monitors.
As for what monitor I'm using, it's this one which seems to be fairly affordable for decent quality: https://www.amazon.com/Sceptre-Monitor-DisplayPort-Speakers-U275W-UPT/dp/B098HQ8...
Also I don't know whether this will help you figure anything out but I think that the lag might be caused by using up an entire cpu core, though I'm not certain whether this was the cause due to some strangeness and me not being very familiar with Python. When I run the game at 4k it uses up a fairly consistent 25% of my total available cpu power (it's a quad core, specifically an Intel Core i5 4670k running at the default clock speed, if that info would be helpful), though when I go to look at specific core usage, it seems to be split across all four cores.