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Not really sure what the underlying question in your mind is here
However in your example - both systems will end up with the identical image scale.
If both cameras have the same number of pixels then both cameras will also have the same total field of view
However the telescopes image circle may or may not be matched to the sensors (since you said they were to be the same) and the Well depth of the 2uM sensor is going to be much smaller and certainly inferior to the 4um sensor and therefore likely have considerably more noise as a percentage of signal - ie Signal to Noise Ratio will be worse.
eg Read noise will be much the same for each and Dark noise too, but total signal will be much less in the smaller pixel sized CCD - based on area but also on the fact that there is some lost sensor area overhead in each pixel too - space for the internal wiring and the boundary edges of the silicon structures and any other etched circuitry.
So the signal to noise ratio will be significantly different - thus bit depth might end up being something like 7/8 Vs 10/11 (I'd need to work it out properly if you're interested)
The point source objects (stars) are still going to saturate the pixels in each system in similarly quick times, but you wont necessarily have the well depth to capture the faint details in the extended objects.
And you wont be able to increase the exposure time on the smaller camera to compensate because it will not have the well depth and hence dynamic range to collect any more photos/electrons.
So having the larger sized CCD is going to make all the difference in your example.
That will provide you with the best result.
Of course this is all moot if the Seeing conditions, light pollution and local conditions are not able to support it and nor is your system choice going to matter much if you cannot track and guide on the object to a high degree
So removing tracking, guiding, seeing errors, low periodic error etc are likely to make a much bigger difference - but I diverge from your posted question as stated, but i do think that is a missing element in what you are hoping to understand.
Cheers
Rally
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