Thanks for the insight, Ben.
The tag on the 2006 version with the comment on down is why I think it was the calendared version of pertex, and why it feels slicker and is less breathable. The process presses and flattens the fibers together, reducing the breathable pore space - as I understand it (hey, I could be wrong!).
For the price, I think the new Ion is worth getting just for a more stealthy color than Orange or Red!
It's interesting that the new Houdini appears to be Epic, or very similar. The infamous Big Sky company had an Epic rain jacket, but it appears to be back-ordered, like their tents.