Looking at your specs list, I could comment that the video card does indeed make a difference when it comes to poser 2012 (and other versions?)..

I recently swapped out my AMD 6950 for an MSI GTX 560 Ti 2GB card and it made a huge difference, mostly because of nVidias drivers when it comes to OpenGL. I found the AMD version of it too glitchy (tried a 4800 series and the 6950 cards..) A 2gb memory video card will allow you to run a higher screen resolution without any lag. I ran a speed monitor on my video card while using Poser 2012 and found that barely 1% is used while rendering and lucky to reach 20% of the GPU's available resources while working in the preview screen with complicated scenes.. so there's a lot of head room there. 

I have my temp files directory pointed to a 10,000 rpm drive which makes loading and changing stuff a lot quicker than having it reside on my 7200 rpm boot drive. I also reduced my 'undoes' to 20 vice 100 which helps too..

What you have to remember as far as hardware and memory is that your CPU is what makes your renderings go faster, not the video card. But as JohnDoe said, the GPU handles the OpenGL in the preview screen and the bigger, faster and better card will make a huge difference in there. 

Your system memory comes into play (in 64bit version OS) when you wish to run several programs at the same time. I often have photoshop, yahoo voice chat, dreamweaver and a browser open at the same time while working in concert with  a buddy who lives across the country. The more memory you have, the better. 

So in short: Go with nVidia video cards, the bigger the better.., max out your system memory, and have fun.

i7 940 12 gigs memory, 4 x 1TB drives, 160G Cheetah, GTX 560 Ti 2GB video card on Vista64 Ultimate. 

I hope some of this helps, its what works for me though your milage may differ.