Noise charts are useless, they are probably stock vs stock and they give no info about the fan profile.
For mid end you cant go wrong with AMD's 6850/6870. But personally I prefer nvidia's 570/580 GTX for quiet high end gaming. For the sole reason nvidia is a better GPU (sorry, I used yo be an AMD fan) and they have more custom cards out. BUT AMD seems to be catching up with things and more customes are being launched lately (HIS IceQ etc.
You can't go wrong with this 580, see my review here:viewtopic.php?f=19&t=62679
Remember that high end quiet gaming is as much about your GPU cooling as it is about your casefans and airflow!
Also you can get a 6970/580 quiet at idle, but not at full load. Therefore not just go for dba but for the gentleness(?) of the fans. That never shows in noisecharts.