P8 renders faster and can better take advantage of new computers with more cores

P8 has other improvements such as lights with inverse linear and inverse square falloff.

P8 has soft ray-traced shadows that don't look grainy, because you can adjust the sampling rate.

There's no doubt in my mind that P8 reduces the effort to achieve realism over P7. And for certain types of scenes, it does things that P7 just cannot do, no matter how tricky you get with shaders.  So I highly prefer it.

Of course, if you're not going to make the effort to learn the new features and use them, then there won't be any difference except rendering speed.

If you're thinking of switching and money is no object (or SM announces great upgrade pricing) I'd consider waiting for Poser Pro 2010.  It has gamma correction, another important ingredient for realism. There are ways to incorporate GC into P8 and P7, but it's just a lot easier with Poser Pro.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)