Hello
Sorry this is late, I just joined the forum after lurking for a year or so.
You should pick the settings you enjoy most. Try playing at 1440p and medium settings to see if that works. After that give 1440p with low settings, 1080p with high settings and 1080p with ultra settings a go. Which did you like best?
I gave up trying to change a lot of individual settings. It felt like playing whack a mole….
You can also try DLSS. This article suggests that DLSS 3 might work okay when playing MSFS. https://www.techspot.com/article/2546-dlss-3/
My system is probably similar to what you have with the exception that your cpu is a bit faster while my gpu is a bit faster. My settings are:
Ultra (really like the visuals) at 1440p
DLSS 2.xx (trying this and TAA to see which works best)
Fps limit set to 50% of a 75hz monitor which equals 37 fps (weak power supply and mediocre case cooling, trying to keep everything cool and not burn up the power supply)
The Sim runs smoothly at these settings.
Running task manager on the second monitor. It lets me watch cpu, memory and gpu load (also gpu temps).
You mentioned the RTX 3090. Have you seen the prices? $1,300+ on Amazon! The RTX 4070 ti looks like a much better deal at $800+. https://www.videocardbenchmark.net/compare/4116vs4495vs4284vs4699/GeForce-RTX-2070-SUPER-vs-GeForce-RTX-3050-vs-GeForce-RTX-3090-vs-GeForce-RTX-4070-Ti
The 4070 ti can get by with a 700 watt power supply while the 3090 needs a 750 watt PS. There is also the question…..will you be able to take full advantage of the card or will your cpu become the bottleneck? https://pc-builds.com/bottleneck-calculator/result/1dv176/1/general-tasks/2560x1440/
Always something with upgrading PCs.
Cheers