As maru and burning wrote ...
A good displacement texture is
A) huge from the start, never scaled up, but not too big so you cram all detail in a small screen space and end up with steps
B) as blurred as necessary
C) 32 bit or 16 bit from the start, never converted from a lower bit depth to a higher one.
As maru wrote:
Give two neighbouring texture pixels enough space on your model and they will unavoidably cause steps.
Overall, it is a balancing act.