So back to the point... I currently have VERY close to your setup (differences are that I'm using a 3570K OCed to 4.3Ghz and a P8Z77-V LK). I just picked up an 8GB RX 480 and wow flies with it. Just a massive improvement over my old GTX 570.
I would, however, advise against the Asus model - I heard that it was loud and ran warm. I got the XFX GTR, but from what I understand the MSI Gamer or Armor are the quitest/coolest by far.