I am using 4K at 60Hz and the sim runs fine. I have 2 addition 2K monitors I used to put the PFD and MFD on. I am not sure I can see much of a difference from 4K or 1440. I have the graphics on ultra and did not change the config file to try and get more. 4K makes a difference with the scenery I am using in P3D so I leave it at 4K even with MSFS 2020. If all runs well in 4K then it is still worth it, I am sure the graphics in MSFS 2020 will get better over time