Hi Toto,
Testing according to your configuration I came up with
TBM 900 = 100 fps
C172 = 100 fps
Rolling back to my configuration: 2xAA + FXAA, full screen, draw shadows on the terrain I got
TBM 900 = 59 fps
C172 = 85 fps
TBM v1.1.1, X-Plane V11.26 and W10
I'm running X-Plane at 1440p, my hardware is in my signature
Hope that helps