Just responding to this topic because I also encounter this small stutter and game slowdown in carreer mode.
my system is as follows:
i7-7700k at 5ghz
16 gigabythe of ram at 3200mhz
and 2 gtx 1080TI msi gaming X in Sli
running at 4k steady 60 fps (vsync off it is 80-120 fps on Kuban)
i have build this rig only for Il2
one thing that helped me is disable Hyper threading, that also made overclocking to 5ghz easier.
I only have a problem in carreer not in Quick missions or scenario’s.
The only thing that doenst’t help is turning off full screen, then I get 30-200 fps jumping like crazy.
Hopefully this is to some use for finding a sollution to the problem for the devs