Some great stuff here Richard...I like the 3rd one best, except for the very long crack running through the entire cliff at the center of the render, kinda distracting the way it looks now.
The others are very good as well though. Each has its own interestingly looking features. The 2nd one has some pretty sweet looking voronoi flattish faces seen in, say, Yosemite.
I don't know what you think, but I think displacement-wise these are 95% finished (it never gets too 100 eh) and shading/texturing will take it next level?