I just got Poser Pro (full), and I find it to be a lot faster than Poser 6. It might be a Mac Intel thing--I also just recently got an Intel iMac--so maybe PPro is optimized for Intel or something and P6 isn't, but on this same machine, PPro is significantly faster than P6, particularly for rendering. That in itself is worth it to me, particularly for animating, since I can now render out test animation without having to get up an go make a cup of tea while I wait.

I also have InterPoser Pro, and find it to be great for rendering my full animations in Cinema 4D. I still use Poser to compose the animations, since the interface is a still a bit easier to use than C4D's for animating Poser figures.

I haven't had a chance to try the Poser Fusion plugin yet, however, since for some reason Cinema 4D isn't seeing it in the Plugins folder (I have a call in with Smith Micro). I'm not sure if I'd end up using it or not. The only advantage I can imagine is that IPP has one flaw in that it seems to have a little trouble interpolating "smooth" spline animations from Poser to Cinema 4D--it tends to flatten the curves out an make the moves jerky--but that can be generally fixed by making sure that you have a keyframe for each frame of the animation for each part that moves before exporting the animation from Poser. That can be a little bit of a drag to do, since it has to be done manually (anybody know an automated way of doing this??) That said, having the figures in Cinema 4D (via IPP) has a lot of advantages, mostly in that your figures can interact directly with their environment, and can take advantage of C4D functions like cloth, hair, etc., plus adding and changing textures is easier and more direct as well.