I have the same setup as you but with an Nvidia 2080 refrence card. I can run P3dV4 nearly at max using a detailed airport and PMDG 777 while maintaining 35 FPS. I do use a 2580x1080 monitor, so a smaller 16x9 widescreen dsiplay will give you beter FPS.
I had this issue in P3D V3. In order to fix it, I used this little utility:
https://library.avsim.net/search.php?SearchTerm=logbook+editor&CatID=p3dutil&Go=Search
Original author has updated it for use in Prepar3d V4.
Can I get some pointers from you folks on how to get CLS MD-80 in P3DV4? I tried installing it and I get no landing gear and the nose gear turned hard to the right. Is there a secret V4 patch?