Your current system isn't exactly going to hold you back much. While it's not going to do BF3 on Ultra with AA @ 60 fps, you'd still be able to play at 1920x1080 on High or with AA disabled.
So, I'd hold off on upgrading until Ivory Bridge hits (at a minimum) and you can take a look at the new offerings from AMD and nVidia on the gpu front.
With that being said if you are just set on upgrading now, which I'd understand,. at normal resolutions nVidia single card setups are king right now. The 570 is hitting 49fps while the 580 does 55fps (1920x1080, AA, Ultra)