For a reference point, I’m running a 4k monitor just one notch below 4k on the sim render setting with no noticable drop in image quality. It’s a 5800x3d, 7800xt, and 32 GB 3600MTs. I’m hitting 45+ natively in most settings with mid to high settings. The only place it’s struggling is at JFK (and maybe other large airports, but I haven’t tested and may also be code optimization related), but even that maintains 30+fps.
I would say something like a 7800x3d (if you can find it reasonably priced), and a 7900GRE or 7900XT should get you there at full 4k native. 32 GB memory would be a good start. I’ve noticed a bug at JFK where it’ll report using more than that in the sim, but task manager shows my memory usage is only about 80%. I think that is also related to the code optimization and bug because the sim never reports memory dropping as I leave the area. If I start in a rural area, memory reporting in the sim looks normal. So maybe consider 48-64 GB memory?