You missed my point entirely. I'll spell it out.
You can cut the pixel linear dimension by a factor of four (giving you four time the resolving power), use NR to reduce the per-pixel noise to parity and still be left with twice as much resolving power.
No, I understood your point (although, I think you mean cut the pixel pitch by two, for four times the resolving power...you can fit four 1/2-pitch pixels into a 1-pitch pixel when factoring in two dimensions...if you divide the original pitch by four, you end up with 16x the resolving power, as you could fit 16 1/4-pitch pixels in the area of a single 1-pitch pixel.) I don't deny that you gain resolution...you do. But there is most definitely an increase in per-pixel noise, which limits how far you can push ISO on the high end before noise becomes such a problem that even with maximal noise reduction, you can't "have your cake and eat it to." You either have very noisy detail, or smooth "pixels" that barely or don't even offer the same detail as a lower resolution sensor. I wouldn't say it is impossible to get small pixels performing on a similar level as larger pixels...assuming you can get enough light incident on the photodiode, you could probably normalize the difference and make the higher resolution of an APS-C perform just as well as the lower resolution of a FF sensor...but we don't yet have that technology in a camera you can actually buy yet, nor will in the near-term future. Maybe if newer technologies quickly find their way into DSLR products, we might see better native-size performance out of an APS-C sensor...but as it stands now, even with NR, bigger pixels are still less noisy...by a factor of 2x or more. Assuming you normalize reach, fill the frame with your subject in both cameras, the higher image resolution of the 5D III means it would outperform the 7D on all levels, including detail and noise.
