It is amusing that the nv boys keep whining about being treated unfairly because the memory size, but fail to mention 570 has 320bit bus width vs 6950's 256bit.
It was the design decision by nvidia to use some non-standard aggressive memory bus width to make up for the inefficient core...
Every card has some kind of inconsistency, for example, the gtx 580 varies from losing to 6970 to 20% faster, that is just some stupid excuse made up by some dumb fan boy.
580 is more like a 485, 15% is not enough for those who bought the 480 to "upgrade", those who did not buy 480 would probably have no interest in 580, all those give you the impression "tons in stock" becausee it does not sell well.
A short while ago the nv fans can kid themselves by thinking fermi have "superior sli scale", it is now been proven false, if the 6800s are not hurting enough, the 6900s are coming within afew weeks.
The nv boys are getting desperate, grasping at straws, spare some forgiveness to them :(