I'm sure I'll get flamed for this and maybe I'm missing something here, but when I compare the D7100 to the 70D and 7D on the graphs there doesn't seem to be all that much difference.
I admit I'm not a dynamic range freak, and I'm more interested in ISO performance, but it doesn't seem like there is any real world difference between the Nikon and Canon sensors.
My conclusion: The 70D sensor offers an almost imperceptible improvement over the 7D and the D7100 might be an equally imperceptible improvement over both the Canon's but not enough to make buying a camera based on the sensor alone worthwhile.
For all the talk about how antiquated Canon's sensor tech is, I'm not seeing it in these results. Even their summary (if I read it correctly) says the Canon and Nikon sensors are only about a fifth of a stop different in ISO performance. One-fifth of a stop?
Okay...I'm waiting for the flaming to start.
Not much for luminance SNR. It's right there with the best of the best D7100. Whatever differences there are you'd never spot.
Tons for DR though and now it's also at high ISO where it is behind for that not just low ISO. The D7100 utterly whomps it for dynamic range. Also considerably for color sensitivity (very oddly though, despite that, the metamerism index is only 2 #s apart this time for daylight and the Canon is actually one number ahead for indoor lighting in terms of color discrimination, I guess somehow it manages to have about the same color discrimination and yet still a lot more chroma noise, in the past when the canon had worse chroma noise it also had noticeably worse color discrimination. Looks to have the same chroma noise as the old 7D but better color discrimination indoors by four points (whatever exactly four points means, that's a tricky element).)
So the 70D seems to be more or state of the art for luminance SNR, reasonably solid for passes for solid these days for daylight color discrimination (although weaker than old stuff), quite strong for tungsten/artificial lighting color discrimination, wayyyyy behind state of the art for low ISO dynamic range, solidly behind the state of the art for high ISO dynamic range, solidly behind state of the art for chroma SNR.
Compared to the 7D alone it appears to improve tungsten lighting color discrimination a fair bit, improves luminance SNR somewhere between 1/3 and 2/3rds of a stop, slightly improves DR at very high ISO (although oddly 1/2 stop worse at ISO200, otherwise appears to be within margin of error for DR), has about the same chroma SNR. It probably has a lot less banding than the 7D though for both low ISO deep shadows and vertical gain banding in the lighter shades. But the random noise at low ISO shadows are still very circa 2007 quality.