(commentary)
One thing I've found myself writing over and over again in response to emails about recent Nikon bodies has to do with the megapixel count. The persistent notion amongst many of you is that fewer megapixels would give you better noise tendencies. Thus, everyone keeps asking for a 6mp DX or 12mp FX body.
In practice, things are a bit different than you'd expect. Unlike Canon, Nikon is using smaller process sizes in their latest sensors. One thing this has done is make the light gathering capability of a sensor of any given size pretty much the same regardless of how many pixels are arrayed on it. A 24mp DX sensor isn't "noisier" than a 12mp DX sensor, and wouldn't be noisier than a 6mp DX sensor. We no longer lose lots of surface area due to data and power lines, for one thing. We lose some, but not enough to matter, really. The improvements elsewhere in the sensor signal processing are more than making up for any loss of surface light sensing area.
That's why if you print an image off a 16mp FX sensor and 36mp FX sensor at 11", you shouldn't see any difference in noise. Yes, the per-input-pixel noise level of the 36mp sensor may be higher in standard deviation measurements, but the per-output-pixel noise works out about the same. Moreover, you have a benefit in that apples-versus-apples comparison: the 36mp has more sampling of the data for the same output. That shows up usually as higher acuity.
The exception to the rule comes if you use those extra pixels solely to print larger. You can't print larger with a 6mp DX camera than you can with a 24mp DX camera, though, so it's a moot point. If you run a 6mp camera to 30" prints, you're at 100 dpi and that's easily in the realm where the viewer can see the lack of resolution. If you run the 24mp camera to 30" prints, you're at 200 dpi, which is above where I'd usually put the threshold of "not enough pixels", but sure, you might see some noise increase.
For most people, though, you're not outputting large enough to worry about noise. If you are outputting at large sizes, just stick to the lower ISO values. None of the current Nikon cameras are wimps when it comes to dynamic range (and lack of noise) at base ISO: D3200, D5200, D7000, D7100, D600, D800/D800E, or D4. In other words, at base ISO I'd take every one of those mega-megapixeled cameras over their pixel underpriviledged predecessors (and any new one you might create). At high ISO and normal print sizes, I'm still better off.
So don't expect Nikon to step backwards with pixels. Not with Bayer sensor cameras.
