I am planing to configure sli gpu on my system. I am rightnow using GTX 560 Ti. With single one I can get good graphic output but I am not getting maximum resolution. I want some help here. It is worth to go with another GTX 560 Ti or should I buy a GTX 590 which is a bit more powerful and better. I am stuck between this two choices. I want to use my existing gpu anyhow for this purpose.