You are going to need more than a 570.
If you want to game at that resolution with modern games at high settings with a great framerate I would say go sli 680 or crossfire 7970.
I have 2 2560x1600 monitors so I know how demanding that resolution can be. Also, it will eat VRAM, get 3gb or more. Keep in mind if you put 2 680s with 2gb vram in sli you will only get to use 2gb of vram, not 4. same works for AMD cards in crossfire.
2560x1440 runs fine on a single 570 here. Of course, my definition of "fine" might differ from yours. I'm not running sleeping dogs with everything turned to max and 16x msaa or anything. But it looks good and runs smooth.
I don't use anything over 2xAA when gaming at 2560x1600. Really depends on the game though. I'm just saying, if you are going to buy a card might aswell buy the best one you can at the time. There are various games that do require a 680 or 7970 to run 60+ at high resolutions.