The 15% number is pretty much established now I think... Anandtech mentioned 15% in their review too. This difference rises in minimum FPS, though, might affect some people's decisions. Obv this means a lower maximum FPS difference, but who cares about max FPS anyway.

btw majord (does this stand for "major chord"? ) about the HWC review. Your numbers show 22% over 5870 for 1920 with 4AA, but HWC's own compilation shows 18%: