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That's an excellent explanation Rick. Fundamentally understanding exposure, the different types of noise and CCD/CMOS characteristics are very important areas. There are a lot of misconceptions and myths around the different types of noise (I have to say that I consider unwanted signal and noise the same thing - not all noise is per definition randomly distributed). There is no one-answer or one formula that will work for all your imaging sessions and every decision you can make will be a trade off.
A mount with a large PE will be a consideration in that trade off, but it will be just one of many factors - it may not be a major factor at all!
Purely mathematically, adding (notice I'm not saying "stacking" here) multiple short frames together is the exact same thing as recording one long exposure. But as Rick so eloquently pointed out; throw the different types of noise in the mix and things become a little more complicated.
One nice thing about having multiple sub frames though, is that, as opposed to one long exposure, you have after-the-fact control of the integration ("stacking"). This allows you to tailor the integration process to the data, gear and its noise profiles.
For example, instead of simply adding the sub frames (which is the same as averaging all frames, then multiplying the result by the amount of frames), there are a variety of other ways to determine the 'true' value of a pixel. Instead of the mean, one could take the median, or the mean of 2 samples around the median, or any other use any other type of rejection algorithm. Using different integration/stacking algorithms some types of noise (cosmic rays, 'hum', inconsiderate neighbors, atmospheric turbulence, etc.) can be better overcome than when using "nature's" integration method.
Cheers,
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