Yeah, I know, you'll all hate because it is from DxO but...http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-cameras-side-by-
The 30D (59) is a touch under the 20D (62) and the 50D (63) is just a wee bit below the 40D (64) but the 60D bests them all. Of course the 7D shouldn't be left out and whilst it scores 5% better than the 60D in low-light ISO, they rate it overall as the same (66). The 7D also bests the 60D in dyanmic range (landscape) but the 60D takes the honors for portrait colour depth (22.2 vs 22).
The other takeaway from this is that both the 30D and 50D were a step down in IQ from their predecessor, so I wonder if the 70D (the next odd-numbered xxD DSLR) will fit that pattern?