Can somebody please point towards a good explanation of DR and also comparisons between similar cameras (e.g. D800 and 5D M2/3) so I can understand it better and how it impacts me? Also any explanation of camera IQ would be helpful.
From Wikipedia: Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity.... In photography the quantity is luminous intensity (brightness) and the end points are the beginning of pure black and pure white. It's generally measured and expressed in stops of exposure (one stop more being twice as much light; one stop less being half).
For example: you take a picture of a beach sunset with the sun, clouds, ocean, beach, cliff, and a cave all in the scene. As you get closer to the sun details get brighter and brighter until they are pure white. As you get closer to the cave details are darker and darker until they are pure black. The range between the point of brightness where detail transitions to pure white and the point where detail transitions to pure black is the dynamic range.
It impacts you because there are scenes in real life with a brightness range that exceed a sensor's ability to record detail. So you either have to expose to lose some detail to pure black, pure white, or both; or shoot multiple exposures and merge them manually or using HDR software.
I'm going to be blunt: like most things in photography, differences between equipment are exaggerated beyond reason in forums and discussions. It's human nature. If you look for it in a RAW converter, there is a consistent difference in DR between the Canon 7D and the 5D2/5D3 of approximately a stop. The D800 adds approximately 1-1.5 more. These estimates depend greatly on the level of shadow noise you are willing to accept for your purposes, something fans in forums never seem to take under consideration. They will howl and cry about differences seen on a monitor zoomed to 200%, and ignore that the differences are nearly impossible to see when you are purposely looking for them
in a 20" print.
The difference is there, and it can be noticed in some situations. But generally speaking you will still get the shot, you might just have a little more noticeable noise / less detail at the extremes. Also, generally speaking, for landscape shots with really impressive DR / noise / detail you will be shooting and blending multiple exposures with any current body.