Thanks all for the replies. I'm only interested in bettering the performance of Microsoft Flight Simulator. According to MSI Afterburner/Rivatuner, my GPU is what is severely limiting performance, as it approaches the high 90 % range, while the CPU usage is quite low by comparison. I'm currently on a 10-year old monitor, 1080p, which still works today. Until it no longer works, I'm not interested in upgrading it, either. At 27", if/when I need to upgrade, I may go for a 32" 4K monitor. This is for a computer desk, so viewing distance is roughly the length of my arm, maybe slightly more. I did upgrade my RAM just over a year ago to 64GB and I've only used about half that amount when purposely throwing everything at it. (MSFS Flight Sim on Ultra plus many browser windows open). I imagine the RAM usage would've been higher, if my GPU hadn't bottlenecked the system.
I think for now, I'm going to look into adding a SSD, particularly if I can get my hands on an 8TB SSD for a good price for Black Friday. I'm currently seeing them for about $650 on both Amazon and NewEgg. I also have a 10TB HDD which is too slow in terms of performance for what I need it for, basically Hyper-V (VMs).