RESOLVED: the stutter in question was eliminated after 1 hour of in-game testing.
Okay, the conditions for removing the lag:
I just got rid of all limiters and anything to do with vsync (.INI files)
only ENB's vsync setting was enabled
SSE Display Tweaks was disabled completely - this mod/fix actually works only for monitors over 60hz and therefore cannot be used with a 60hz monitor connected to HDMI
Havok fix enabled
SSE FPS Stabilizer disabled
Skyrim Realistic Overhaul disabled (to reduce VRAM consumption as much as possible)
I hope these findings should be of help to anyone using a system setup similar to mine.
sa547's post in Unexplainable camera look stutter after 45-50 minutes of gameplay. was marked as the answer