its not an easy answer, why you may ask, well for P3D we all know that its uses more CPU, so higher than 1080 is wasting money, 32GB RAM its mandatory on all systems otherwise the PC is bottlenecked.
the SSD for OS must be not less than 500GB, why, because all goes to P3D addons on C: and another SSD for the simulator 2TB minimum.
i'm not an expert however my comments are based on my experience and in what I have watch and read.
There're several places where we all can have a look and you will see that there is no consence