I'm running a GTX 560 ti with 1.25 GB VRAM and an Intel i7 2600, running off an SSD with 256GB
I get good results with Firestorm ranging from 40-80 FPS. SL viewer 2 gives me 20 or less.
Hope this helps. I took ages trying to decide on the video card and whether to go ATI or Nvidea.
Mark