World Machine/Blender seems to be working fine, but this is just a standard 2m square plane. The one I tried yesterday was much bigger than that because I wanted to create something more resembling a terrain, in km rather than m. Scaling it once the material is applied works, I guess that might be the best way to go. If I then apply the scale it flattens out a lot but I can fix that with the scale slider on the displacement node. I’m just not sure how materials and particle systems would apply to a scaled object. More research needed on that.
I also increased the contrast of the exr in GIMP. Krita wouldn’t open it due to ‘unsupported color space’ but GIMP had no problems, so no big deal. I must admit that even a 2k exr gave decent detail. I suppose it will depend on how close to the terrain the camera is. If a fraction of it is filling a 2k render area I might need more resolution in the displacement map.