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.
There's a small real world difference in terms of IQ when you have to dig really deep into the shadows. It's blown up into a huge difference by...
* Shooting a wall in the dark.
* Shoving the exposure slider to +5 EV.
* Turning off all NR on the Canon sample.
If you normally shoot this way, Nikon is your first choice.
I was already on FF when 7d came out but through the years i had a chance to review files from assistants, friends & gfs from either 7d 60d or d7000 (have to find one with a pentax now
The IQ difference isn't that tiny really. First you can get really nice files out of those sony sensors below 400. You can get FF quality easily, whereas 7d really has noise all over the spectrum. You can see a quantitative difference with local adjustments of about 1-2 stops and what happens to color and noise.
Obviously you can see a massive difference if you want to salvage shoots where flash or strobes didnt fire; basically those sony sensors are isoless, you could push an underexposed iso100 all the way to 3200 and there isnt much difference from a native 3200, plus the tonality will be actually greater.
From someone coming from compacts or cameraphones the difference is nonexistent but from someone who wants too squeeze every possible drop of quality from an apsc sensors, then you'll find canon isnt your best bet.