[Stefan Buda]

Peter you are absolutely correct about the physics.
That is why I was talking about "practical size domains" in earlies comments.
That is why I tried to restrict the discussion to comparing an 8" to a 16".
Francisco is talking about a scaling factor of more than 3x, involving an increase in light gathering of 9x, and that is pushing it a bit. But even so the difference between the two setups will not be very obvious when it comes to S/N ratio in extended objects.

EDIT: I got it wrong.
Exposure time would be the same if we used the same sensor on both scopes. Because we are scaling up the sensor as well, as Francisco suggested, the exposure needed to achieve the same "depth", becomes significantly shorter.

The bottom line: The larger setup, despite of having the same field of view, would have somewhat better resolution and would record faint nebulosity significantly faster.