I'm sticking with Poser Pro for now because of the multi-thread rendering. I can build massive scenes Poser 6 couldn't handle. Then PPro with 4 cores renders lightning fast. But I do comics and time-saving is a big consideration for me.

Poser 8 has more realistic rendering capabilities.

It probably depends on what your needs are for which version to choose now.

I'll definitely grab Poser 8 Pro if it also has multi-thread rendering like Poser 7 Pro.