Thanks all for the comments and advice, I do appreciate both. Su liam it was simple Ridged perlin from Terranoise. I dont htink I tweeked the roughness settings. I then brought it into Gimp. On a layer above it I rendered clouds as detailed by RobA in his tuts the blend mode was "overlay" in an attempt to get a bit more roughness. It was still a bit smooth so I increased the roughness for the mountains by using an additional bump map based on the mountain texture itself.

By "clipping" do you mean the flat top on the mountains?

Torq