I just got to make my flying much better this weekend following the suggestions above. So, I would like to make this public to help somebody else get good results from Prepard3d 4.5.
My system is composed of a Main Board ASUS B450 processor Rayzen 2700X 16 cores and a video board NVIDIA GTX 1070, 16 GB main memory, four monitors connected, one of them with VC, and other with external plane view. The other two monitors run with auxiliary 2D screens. Resoluiton 4k on the main monitor.
I was even used to fly with 8~10 fps in very difficult way, having to turn everything off when departing and landing.
Then I read the considerations above and had a wonderful progress. Using affinity mask of 65535 and FIBER_FRAME_TIME_FRACTION=0.1, everything else made minor minor changes. I more than doubled FPS as a result and now can play freely with the other settings, putting the cursors to the right for all settings, having even Airbus 319x and 320X from FlightSim Labs running smooth with no shaking in approach and depart any more. I also limited FPS to 24 to free CPU power for use at around 90% on core 0. This caused the Video Board to present to work more effectively, now loaded with more than 70%. No problems with cooling, air in my case, with the boards raising to around 70 degree Celsius. I understand that for flight simulation you do not need more than 24 FPS.
Before this changes, the boards seemed quite lazy, with 20~30 percent load.
Hope this helps somebody. I was tired of having inefficient advices from the Internet, and people saying "my system runs at 65 FPS steadily, I made this and this and this". I do not believe that !