Don't know how much faith to place into this, but the prices are listed in of those posts. The 6970 is going to be the same price as the 580 @ $499, so the performance should be near identical. The 6950 is going to be $375 (if the coversion is correct).
http://tech.163.com/digi/10/1202/16/6MTNAIP9001618J1.html
The performance part there is pure speculation, but looks like the 6970 will be able to compete well with the 580.
If HD6970 is priced as GTX580 it will be a major disappointment if isn't a clear notch faster than it.