How much AI traffic do you have around you? Tracking of Ai aircraft costs CPU time every frame, and with around 250-300 active aircraft ( so not in slep mode) in the reality buble eben an I7 is at its end.
For future versions of P3D, I recommend that for the tracking of AI aircraft you introduce a sort of LOD system - only very near aircraft are handled every frame, aircaft at the edge of visibility every 8th frame is enough and beyond that, and there is the vast majority, even every 32 frames it is enough. With my AI traffic for ships, running on a simconnect client instead of inside P3D, I could reduce the CPU load a factor of about 10 doing so.
Since you dicussed the affinity mask, my experience is that using a mask=1 I get slightly higher frame rates than with any other setting, ( the CPU goes into automatic overclock), but loading takes much longer.