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Filtering quality of 7 series is improved over 5 and 6 series, and is on par with GTX580, but AMD use a slightly more aggressive neg lod bias by default to create a slightly sharper image; at the expense of slight shimmer/noise. You can clamp neg lod bias on the 580 to further reduce shimmer/noise.
Is this your only argument? It seems you've been reduced to the same old tired statement over and over. Shimmering is not an issue for ATI, every once in a while, you may see a driver update that has an issue with this, but it happens with both camps. Sometimes mistakes just happen in a driver update, and it does happen from both camps.