Well my res is 1920x1080 for the single monitor. As far as budget I don't really have one, this was offered to me as free. The single 560Ti is performing quite well actually, still giving great fps in all games I play. Just getting it for free and wondering if its worth doing SLI and 3 screens.
Sli'd GTX560Ti's are pretty potent and I have had no issues in the year and a half that mine have been running.