Well, you are right that Poser won't utilize the GPU for rendering but it still takes care of the preview window using OpenGL, so just keep that in mind when considering cards and OpenGL support for large scenes.

 

DDR3 is still cheap as hell iirc so I'd go from 8 to 16GB not for Poser but for Vue since it's such a memory hog. Otherwise the specs look good and you'll probably get a lot of mileage out of that setup.