Heya
Its hard to advise out of thin air, I would need to know roughly what u work on and how to advise… Basically speaking u are looking at 100mb of GPU memory per 1 million polygons (or at least that what was 1 year ago).
Every 2 GPU based graphic card has only 50% of its Memory usable. They dont share memory which means u have to fit all in half so that each GPU can work on scene.
Also GPU rendering is missing a lot of features and as far as I know textures are still down sample (its soon to be changed…) So its tricky one to use GPU for production…
The only reason I would use GPU is to do a session with client, set the light mood etc etc what he wants to see and then work on CPU…