Guillermo, thanks. I do understand that. You're pixel peeping though. I'm looking for practical examples. And maybe this should be a separate discussion because it's beginning to hijack Nigel's original question.
When I say 'practical', I'm talking about images viewed in real world conditions, not at extreme magnifications on a computer screen. Will a client see the difference in a small image used in a brochure or on a website? Will the difference be seen in a full HD video clip? Will the difference be evident in a print hanging on a wall behind glass at normal viewing distances?
Francisco, that's what I was getting at with the concept of a 'library' of dark frame images. How important are exposure time and temperature from, again, a practical standpoint? Can, for example, you make a series of images at, say, 10 or 15 or even 20 degree temperature differences? 20 degrees may be stretching it a bit. Or can you have a set at, say, 30 sec, 60 sec, 120, sec, 5 min, 10 min, 30 min, 60 min as opposed to every shutter speed in between?