are you actually saying that a gtx570 is not enough to stay above 60fps in Borderlands with 4x AA? I really doubt AA would bring you down below 60fps in that game. if you are going below 60fps then its probably a spot where there is some very unoptimized dynamic shadows which does happen in that game.
I fired up the game at 1920x1080 on max settings with 4x AA with vsync off and framerate cap off just to take a look.
ran a bench with lots of action it and some running around got this:
Frames, Time (ms), Min, Max, Avg
22861, 195017, 70, 165, 117.226
resized screenshot
image hosting png
boarderlands runs great at 60fp no dips at 1920x1200 at 4x fsaa. If i run into certain areas it does bog down to 45-50fps anything higher than 4xfsaa, but wont do it at 4x fssa.