Having read the thread, I may have missed something, but I don’t really understand what problem you are trying to solve…or why the monitor you have isn’t suitable.
I’m no expert, and this is just my opinion based on the experience I have. Firstly, flight sims, MSFS included, actually have pretty modest monitor requirements unlike a lot of “shooter” games where rapid response time and high refresh rate are required. You don’t need a 120mhz monitor to run the sim that will likely never approach the 60mhz of the most basic monitors available. Same with Vsync/Gsync. My perhaps faulty understanding, is that you only need this if your “game” and your other hardware are capable of generating more fps than the refresh rate of your monitor.
The main, and possibly the only monitor-related performance factor, is the number of pixels your gpu is pushing. I don’t see any reason your rig can’t drive your monitor at reasonable settings and at it’s native resolution. Keep in mind, that any other monitors you have connected also have to serviced by the gpu. If you can, you should always run a monitor at it’s native resolution. So 4K gets you a nice picture, but is very hard on fps, while 1080p gets you lots more fps, but picture quality and the field of view is compromised. IMHO, at this point some version of 1440p is kind of a sweet spot.
Again, IMHO, anything above 30fps in MSFS, so long as it is smooth and stitch-free is perfectly fine. I have the Samsung 49" that is similar to he one you asked about, except it’s 1440 vs 1080 vertical (5120x1440). I get smooth flight at low-30’s in Ultra and low 40’s in High…I find this just fine.
So…trying to find the bottom line here, if you want to concentrate on MSFS, use the monitor you have, do without the addon 4k monitor if you can while “flying” and run your present monitor at it’s native resolution. The only thing that really counts is how many pixels you are driving and a fancy monitor with low response time and massive refresh rate will do nothing to improve your MSFS experience. (Different discussion if you may want to get into more mainstream gaming).
My opinion FWIW…hopefully helpful. Cheers.