Wise decision!
Out of personal experience (I have been building my own rig for the last 25years, last 6years SLI configurations), the cycle of graphics cards is about 1,5years. Every 1,5years the new GPU has twice the performance for the same price.
It thus makes it impractical to buy a second GPU even if it is cheaper, because the performance will not be there (compared to the GPU cards available at that time).
Especially for this game it will be the case: The game requires 2,1Gb of VRAM and higher and much faster GPU performance than currently available in the market. My prediction ids that the next (or over-next) GPUs will show a 50% increase in performance with this particular game and these will be the graphics cards we want to have!
My 2cents only, I do not work for ATI or NVIDIA nor do I sell hardware
so, everybody does what he thinks best.
~S~