Good news!
I was comparing my setup against a friend’s one with a very similar system (but he was getting much better CPU frametimes) and the only thing different was he had virtualization turned off.
Guess what? I disabled SVM in BIOS and I’m now getting much better core utilization. That main core is now on 90% instead of 70, 75%. My CPU frametime dropped from 24ms to 17ms (paired with my GPU’s) and the FPS increased from 38 to 52 around the same spot.
Here’s a new screenshot, more or less on the same place, time and weather. I haven’t changed anything on FS settings between the first screenshot and this one:
Pretty happy with the result and I leave that as a suggestion for people struggling with CPU limits. Try disabling virtualization on the BIOS (SVM/AMD-V for AMD and VT-x for Intel) and see if it makes a difference. Solved for me.