I have been thinking about it a lot and have some personal educated opinions. I believe that the higher end Kepler cards will be out sometime in the summer which means that there will be some nice iterations of the 28nm process by the end of next year. Having said that, 2 GTX 580's should outperform every single GPU Kepler card, maybe besides a dual GPU card (GTX 690?) and higher end SLi variations (GTX 680 SLi / GTX 670 SLi?).