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NEX-7 doesnt have weakest AA, then it has really thick UV/IR and SMI of 85/80 which indicates usual Sony high quality CFA. All these things prevent some of the light to get to the sensor.
D7100 doesnt have AA, UV/IR no clue, but since it doesnt make any issues, its simply there and doing its job, SMI is 79/76 which means usual Nikon survivable quality CFA.
As far as noise goes..
ISO 100 (78) - 35.9dB
ISO 100 (69) - 36.3dB
and dynamic range
ISO 100 - 12.59eV
ISO 100 - 12.92eV
Yea, huge difference. Close to not visible. If you add on top of that NEX-7 being mirrorless and not exactly thick one (less space, more electronical noise, less place for high quality compomenents, more heat etc.).
My summary is, that if everything was same, just it was Sony sensor in D7100, then D7100 would have actually better output than it has.
Given Pentax really knowing how to use Sony sensors and it wont have AA, CFA will be probably somewhere between NEX-7 and D7100 (I hope it will), then I really doubt it will be bellow D7100.
If you saw some big difference between NEX-7 and D7100 its result of processing (or not processing) and shooting. Cause there really isnt much difference..