The card you have is more then fine for P8+. I don't think you will see much difference when buying a new one. Poser is kind of outdated, even with the updates made in P8+, when it comes to OpenGL. It's still not using the full power and all features. That's why an 'older' still works fine with P8+

If you use Vue, Carrara and such then a new card will make a difference.

Artwork and 3DToons items, create the perfect place for you toon and other figures!

http://www.renderosity.com/mod/bcs/index.php?vendor=23722

Due to the childish TOS changes, I'm not allowed to link to my other products outside of Rendo anymore :(

Food for thought.....
https://www.youtube.com/watch?v=pYZw0dfLmLk