Hey Kari,

It might not be totally analogous, but what you are describing is similar to discussions I've seen for astro work. Of course, astro work could be stacking images or single exposures, but there is a lot of good discussion.
http://dslr-astrophotography.com/iso-values-canon-cameras/
https://www.diyphotography.net/find-best-iso-astrophotography-dynamic-range-noise/


Both those links get into the whole ISO-variant vs ISO-Invariant discussion. The first links to a pretty good discussion of ISO that pretty emphatically states that ISO is just Gain/amplification to the analogue signal:
http://dslr-astrophotography.com/iso-dslr-astrophotography/

I am curious where you end up as we are both shooting 5DIVs. I do not often shoot nightscapes, but would love to shoot more, so anything you can pass along would be appreciated.

For what it is worth, and this does not seem updated, but a few years back, over at Clarkvision they settled on the 7DII for their low light work:

http://clarkvision.com/articles/characteristics-of-best-cameras-and-lenses-for-nightscape-astro-photography/

Basically, very little dark current noise at given temperatures.


Brant