As far as i know, you can't manually set the strength of a crease. I have been annoyed by that too . You can do a partial crease Edge/Vertex but that is exactly half-way between full crease and no crease. A way that I have used is to refine the mesh (add some more edges close to the one to be creased) then do a partial crease on the edge - it will come out sharper. You need to play around a bit to find what works best.

Maybe someone knows a better way to do this?

About your question on the distortion... I can't think of a simple way of avoiding that. I'm not exactly sure what's gone wrong... perhaps it would help if you could upload a pic of the wireframe.