Really? Then why does an HD5970 have reduced core and memory clocks compared to a standard HD5870?The 5970 is a 5870x2. A 470x2 isn't a very compelling card. Yeah, it's theoretically possible but to me the whole draw of Fermi is that it's #1 for performance and a 470x2 would be beat by a 5970.
The HD5970 is the HD5870 GPU at HD5850 clocks. Even ATI haven't made a full top end card as an X2. Which also means there's no reason why a GTX470x2 wouldn't beat it (GTX470 being between an HD5850 and HD5870 in performance, and half an HD5970 also being between them in performance), since 1) it would be equal in speed outright (GPU vs GPU), so 2) it'll all be about scaling and which games scale well or have issues.
At 2560x1600 (according to the AT review upon launch), the HD5970 was equal to or slightly slower than HD5850 in Crossfire, so it was even worse in performance than the specs might suggest.