Excellent article, but a bit daunting for someone who may be just trying to get beyond the overall scores which are weighted and sometimes a bit misleading.
I would take issue with the following comment;
Another way to look at the relevance of resolution: nowadays, unless you use expensive lenses on a relatively cheap camera, cameras tend to have enough resolution to handle what the lenses can project onto the sensor. And for most uses, 12-18 MPixels is more than enough anyway. So a properly designed noise benchmark can be used to predict image quality as long as you keep an eye on whether you have enough resolution for your needs.
I'm not happy with this concept that a camera can have enough resolution to handle what the lens can project onto the sensor.
The recorded resolution is always a product of both lens resolution and sensor resolution. Increase the resolution of either one, and the recorded resolution will also increase.
In effect, when one upgrades to a sensor with more megapixels, one automatically upgrades all one's lenses as a free bonus.
To take an example from DXOMark's lens database. The relatively cheap, standard Canon 50mm F1.4 on the 12.7mp 5D has a resolution of 55 lp/mm, according to DXO's methodology.
That same lens on a Canon 5D3 with less than double the the pixel count of the 5D, has a resolution of 63 lp/mm. If the 5D3 were to have the resolution of a D800, ie. another 50% increase in pixel count, that same lens would have a recorded image of perhaps around 66 lp/mm.
The point I would make is that probably no amount of money could buy a 50mm lens that could deliver 66 lp/mm or even 63 lp/mm on a 5D. Such a lens has not been produced.
The presence of more pixels on the sensor also has the effect of upgrading one's lenses in terms of the range of effective focal lengths in relation to the standards of a lower pixel-count sensor.
For example, supposing one were to consider that the 16mp of the Nikon D7000 is sufficient for one's purposes and that the 36.3mp of the D800 is far more than one would ever use because one never makes prints larger than A3+. How short-sighted would one be?
What the upgrade from a D7000 to a D800 does in effect, is not only upgrade the resolution of one's lenses, but also effectively converts all one's prime lenses into telephoto lenses in relation to those standards of the lower-pixel-count D7000, and extends the range of all one's zoom lenses in relation to the standards of the D7000. Such an upgrade is almost priceless.
For example, a 50mm, high quality prime on a D800 becomes in effect an extremely high quality 50-75mm DX zoom by D7000 standards.
That great lens, the Nikkor 14-24/2.8, on the D7000 becomes effectively a 21-36mm DX zoom. However, on the D800, by the DX standards of the 16mp D7000, it becomes a high quality 14-36/2.8 DX zoom. No such lens exists, and if it did, it would be hugely expensive at the same quality.