Hi. To avoid misunderstandings, game is using all your cpu cores. It´s only that it has 4 main threads: one is scheduling tasks to the others, one is dedicated to rendering, one to scenery and so on. But all your available cores are used to perform those tasks, so I would not limit your cores or disable HT. How cores are used was explained by devs in last stream.
Regarding the performance problem, are you using >100% scaling in game settings? If so you are requesting your system to work at resolutions higher than 4k (8k if set to 200%). That could be simply too much for the HW. The rendering scale is mainly intended for 1080p resolutions, to get better visuals by rendering at 4k and resampling to 1080p, as Nvidia DSR does.
Check your resolutions using the fps counter in the developer mode to be sure you are not pushing the card too much. I see in the video you run at 110%, so you are trying to go over 4k…
On the other hand your fps will be limited by Vsync if you are forcing it on Nvidia panel even if disabled in game as shown in your video, as game currently uses your desktop refresh rate. So, if you have set refresh rate at 144Hz it will try to achive 144fps, 72fps, 48fps, 36fps, etc, so going to next lower step everytime if performance can´t be maintained. Try using lower refresh rates to release workload and to ensure you can stay on your lowest acceptable fps target most of the time. The list of fps targets is next:
*** 144 Hz ***
1/2 72 fps
1/3 48 fps
1/4 36 fps
1/5 29 fps
1/6 24 fps
*** 120 Hz ***
1/2 60 fps
1/3 40 fps
1/4 30 fps
1/5 24 fps
1/6 20 fps
*** 100 Hz ***
1/2 50 fps
1/3 33 fps
1/4 25 fps
1/5 20 fps
*** 85 Hz ***
1/2 42 fps
1/3 28 fps
1/4 21 fps
*** 60 Hz ***
1/2 30 fps
1/3 20 fps
1/4 15 fps
In my case (2080Ti at 1080p with 200% scaling) I found my system works well at steady 40fps in most cases. So I decided to use 120Hz as my desktop refresh always, using the 40fps target limit (the 1/3 step). When performance drops it goes to 30fps (the 1/4 step) but usually it does not go lower than that, which for me is more than enough.
The 50fps cap seen at the end of video could be that you are staying at the 48fps cap if you run at 144Hz, that´s why you see this limit, as system can´t reach 72fps, which would be the next higher target. I also noticed that in my case, cause I also started flying at 144Hz and went crazy as you trying to figure out what was capping the fps even on lowest settings.
Cheers