Hey!
Do yu know this solution www.romocut.com
It was an exclusive polystyrol milling tool.
Now it is ready for CLAY as shown at the EMO.
The salesman told me that they will be present at Euromold, next december in Frankfurt.
I know that this system is already used to Peugeot, but i don't if it is for Clay or Poly.

I saw it at Euromold and the result in foam was quite good, but I´m not sure what it is like in clay. Additionally it´s range is very small.
But there was some other solution that looked really impressing: Kolb StudioLine.
Check out this video: http://www.youtube.com/watch?v=72SOcRv6pjE