Oops. I've fixed the last link now.
Recently I had an idea of making large features using Perlin Ridges or one of the Perlin Mixes (~1500m) and warping them very heavily to form the basic shape of the cirrus, then merging the result with medium regular Perlin/Perlin Mix features (~300m) which are also warped, and then merging that result with small Ridged features (~40m).
The merging of Ridged-Mix-Ridged or Ridged-Original Perlin-Mix should in theory give some variation and make the result look somewhat like the second picture but unfortunately, so far that's only been in theory. In practice, my results look obviously merged or warped.