Update: DxOMark removed the Nikon D5100 reference from their website.
DxOMark included the Nikon D5100 in the conclusion section of their Canon EOS 600D review:
"The new EOS 600D brings no improvement over the 550D other than a few features. The two sensors perform exactly the same, and show the same persistent noise problem in dark areas at low ISO speeds, preventing it from achieving good dynamic range metrics. By contrast, Sony’s new sensors have efficiently solved this issue, and it will be interesting to see how Nikon’s D5100 performs. Competition may be tough between Sony and Nikon, but Canon continues to lag behind them both."
Maybe they are already testing the D5100? They included the D5100 also in the introduction section:
"On the other hand, the Nikon D5000 could stand against the 600D, but it is slated to be replaced by the newer D5100 very soon."