So I bit the bullet and bought the 13900K(F) because I had two good justifications 
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The PC is also used for 3D rendering and video editing, so even if performance gains in FS2020 isn’t impressive, my 3D apps and video editing will surely benefit from the new chip
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The same shop (in Singapore) where I got my 12700K is willing to buy back my now 9-months old 12700K for slightly more than half the original price! So it’s a good deal for me!
So I plugged the new chip this morning after upgrading the mobo BIOS and boy am I impressed!
At full ULTRA in 1440p (TLOD 200) with FSLTL Traffic and weather, I get a consistent 18-22 fps gains over the previous chip in FS2020 with view panning now becoming much smoother, though the first time you pan in a direction will cause some micro stutters. That’s about 60-70fps for the c172 over lower Manhattan, 52-56fps active cockpit view in the Fenix A320 in my local Airport with traffic and weather, 60-65fps external view in same airport. This are just my preliminary results without doing much tweaks. If there are further improvements I will update this thread.
Test aircraft: c172, FBW A320, Fenix A320.
nVidia Driver: 528.24
Strangely, DLSS still does not make any difference in fps, in fact in some areas I lost about 2-3 frames. Moving to DX12 also dropped some 2-4 fps so it’s still DX11 for me.
CPU Utilization: Between 35-45% depending on aircraft and area.
GPU RTX 3080 Utilization: Between 82-100% depending on area and view
Max CPU Temp on air cooling (no OC): 78 deg C
Do I think I still need a 4090? At this point and this performance, No. Unless Santa comes in early this year 
BTW, my 3080 is the 10Gig version.
Cheers
Santi