Thanks everyone for the replies.
Yes, I finally think I’ve found the balance point; but I was interested in understanding why, since if I lose it, I can know where to look for it.
It seems clear to me, at this point, that the run-up to the highest possible fps makes no sense. Compared to video, with 30 fps (monitor refresh rate 60Mhz and fps locked at 50%) I don’t have a smooth experience; but this I think depends on the fact that this frequency is too low for my monitor. However, if I switch to 80 or 85 Mhz my system guarantees me a fixed 40 (or 42.5) fps and excellent fluidity.
At this point I can push the settings until I see that my system is struggling to reach that number, but I must say that at the moment I can run the SIM with ULTRA settings in almost all parameters, limiting the TLOD to 160-200, depending on the aircraft and the scenery.