Welcome to Tom's Forum!
If you meant advantages of Sandy Bridge CPU with either AMD/ATI GPU versus nVidia GPU then the primary advantages to nVidia GPU(s) are: Scalability (multiple GPUs), cost per FPS, 3D, PhysX, longevity, lower temps, better efficiency, etc to name a few advantages. Today...Tomorrow only testing and reviews will tell. ATI has advantages too like easier to CF, AA and higher sampling details.
It depends on what floats your boat.