I have the same problem with an 6950 too, the flickering and artifacts seem to dissapear if I disabled the AntiAliasing.
Im forcing 4xAA and 16xAnisotropic filter using an utility called RADEONPRO, it worked ok with 11.3 and 11.14, but with the latest 11.5a(hotfix) they seem to have broken something.
For now I just disabled the AA waiting for a solution
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