I never saw PP so I can't comment on that, but the appalling materials editor in Poser 4 really hamstrung the program. Plus the fact that the library system was designed without any idea of how it would cope with thousands of files. Improving those two features really elevated Poser 5. Poser 6 as far as I'm concerned is mostly a bug-fix for Poser 5. It's a bit slicker.