I was also getting a little bit of stuttering from the start, then extreme performance degradation after 2 hours, which became unplayable at 2hrs 13min. Have attached a picture of my display setup, as displays and lighting tend to be the most common cause of performance degradation in an aircraft.
Also for reference; R5 5600X / RTX 3060 / 16GB RAM, 3.9k total hours in MSFS - Sim was using a normal amount of memory and cpu usage throughout.