>The d600 has less MP density then my 12MP d500. The D800 has >similar MP density to the 16 MP d7000 and significantly less >than the d5200/3200
I assume you mean the D50. I don't think the D600 comparsion is accurate. The D600 pixel density is 2.83mp/sq cm. The D50 is 1.65mp/sq cm. OTOH, if there's a D500 out there, I want to know about it!
I think you're basically right about the D800 vs D7000 though. The D800 is 4.22mp/sq cm and the D7000 is 4.39mp/sq cm. That tells me why the sloppiness I eliminated from my handhold technique along with a generally faster shutter speed setting when using the D7000 works perfectly for the D800 too.
All the Nikon 24mp APS-C bodies naturally have the same pixel density of 6.59mp/sq cm. It also explains why, at 24mp on an FX sensor, the D600 is a forgiving performer for a lot of photographers. Seems as though 24mp on FX is an ideal combination of resolution and handholdability (I don't think that's a real word).