Well, the Portras (160 and 400) were revamped in late 2006 to version 2. In early 2008, the 400s were revised again, giving us 400NC-3 and 400VC-3. The 160s were not revised at this time. Here's a Kodak document describing the new 400s.
From what I understand, 800 is on it's 3rd revision, though only two have been labeled (800 and 800-2). 800-2 was supposedly revised at some point, but the label stayed the same.
So as far as I know, the most recently updated Portras were the 400s. Followed by the 160s, then by 800. As far as generation of tech, it looks like the 400 is out in the lead, with the 800 and 160s on the same level.