Got the CPU since two weeks now but only got to get deeper into since that weekend. There is a problem that wasn’t there before: I have very regular stuttering like every 0.25 seconds. It’s nicely visible on the FPS graph and is only main thread. This happened after the upgrade and it’s only FS. I was running the system without PBO, XMP and ReBAR back then and already there the behaviour was obvious. Turning the previously mentioned options did not help. I tried with DX12 and DX11, no improvement. The interesting thing is that the game will start quite normal without stuttering (hangar for example) and then, at the first jump into the cockpit, the stutter starts immediately, turning the PC into a cricket as the coils on my 6900XT are very audible and thus produce short “singing pauses” between every stutter.
I have to investigate further but my guess is FSLTL is the culprit because, as soon as it starts injecting, the rythmic spikes in the main thread appear and do not stop anymore. Also when leaving a flight and returning to the main menu, general performance as well as the globe view tanks from 144 FPS to around 20 to 30, sometimes even less than 10 when FSLTL is still runing. On some occasions I also made the observation that FSLTL sticks a plane “through” the globe. When I zoomed out further, I noticed that it was not only one but like a bazillion planes stuck into each other, “penetrating” the globe 
Something similar happened also earlier this year sometimes when FSLTL was populating an airfield and playing its FR24 routines: in some cases when departing or landing, I would run into such a pile of planes, tanking the performance heavily besides and always parked in the middle of the runway. I also use AIGround and AIFlow to keep FSLTL from going crazy but apparantely, these don’t help.
Did some of you make similar observations?
EDIT: Probably solved! I think have to take back my rant. I am going to assess a bit more but the problem seems to have been a PBO2 which was adjusted a tad too lean with -30 in the Curve Optimizer. I put it to -25 and now everythings seems to run just fine in a traffic heavy environment of Orlando Intl. With DX12 I could gain another 5-6 FPS and I am now between 40-45 FPS in a very big and busy airport and very happy. The CPU swap in general gave me another 15 to 20 FPS in the game. The thing in the screenshot however is an original FSLTL “feature” and stops as soon as also the injector stops. Do the devs know about that?
And just out of interest: which PBO settings do you guys use? I am currently running
PPT 100
TDC 70
EDC 100
CO -25
Should I still crank that up a bit?