Brendan,
I use the same machine as you, with a bit less RAM, but a Radeon 5770. I've upgraded the video cards in this machine several times since it was new. From what I'm seeing, Renderworks will use the machine's core processors, Open GL will use the GPU, anything else is stuck on a single core. Which for us in entertainment, where line renders are a must, is a huge disappointment. Even wireframe refreshes when panning or zooming a document with imported symbols is a train wreck.
I would say save your money until NVW updates the code to actually use the cores and the gpus, because right now, it does not.
Nick