I do suspect this is incorrect. SLI scales much better than crossfire. SLIed GTX 470s are notably better than an HD5970 and probably faster than 2 HD5870, or at least their equivalent but for $200 less.
The best all around option in terms of performance, price and power/heat is two GTX 460s in SLI however IMO. They are on par with an HD5970;http://www.xbitlabs.com/images/video/gf-gtx460-sli/1920_total.pnghttp://www.xbitlabs.com/articles/video/display/gf-gtx460-sli.html
That's tested with Catalyst 10.7, with 10.8 + 10.8a CF profiles, the results are different especially in AVP and BC2 which both gain a signicant performance boost.http://hardocp.com/article/2010/08/26/ati_crossfirex_application_profile_108a_performance
Overall SLI scales better in most games, but it depends on the drivers too.
But I agree that GTX 470 in SLI beat 2 5870's in almost all games, thanks for clarifying that.
That article compares 2 GTX 460 Super OC'd with 2 5870's,if they both are at stock speeds,then the results may differ.
I actually was comparing them ascendingy.