I think that Poser 7 is better than P6 and the service release patch solved most of my issues with it that I had.  If you have a multiprossesor computer it definitely renders much faster.  The multiple undo is great and prevents a lot of frustratons.  

I know you've essentially made up your mind, but you can always try the  P7 demo and see how it runs on your machine before making your final decision.  I've learned a while back that buying outdated software is rarely worth it, unless you're using it to upgrade to a newer version :0).