CPU & GPU underload - low fps

P3d2 is notorious for maxing out CPU core 0 at 100%. This is where it's main thread resides by default and changing the Affinity Mask only shifts the burden to another CPU core. Because these days people have CPUs with 4 or more cores, the total CPU use is limited by the core that is running the main thread. Thus, total CPU utilization rarely exceeds 50%. That's just math and the nature of parallel processing.

Since some image quality settings in P3d stress the GPU and others stress the CPU main thread (like Autogen density, LOD and AI Traffic density), it's difficult to find the sweet spot between frame rate and image quality.