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Good question Markus! I can't answer you directly, but I was doing some related analysis this morning which I thought I'd contribute.
I've always favoured shorter exposures because I seem to get sharper images with them. My recent images for example are composed of 120s subs and captured with a very low read noise, high QE CMOS sensor. I figured I was trading SNR for sharpness and I can always get more data and I loathe blurry images so it was a pretty easy decision.
I had a thought this morning though... even if I get equivalent SNR through more shorter subs, if the target has dim sections that are closer to the noise floor, will I find it as easy to bring out?
I think the answer is no. Looking at a recent image I picked a few areas and gathered some stats from my L master (after calibration of course):
Background: 442 ADU, 3.68 ADU/s
Dim but easy enough to pull out: 489 ADU, 4.075 ADU/s
Dim but could only *just* see in my stretched image without exacerbating noise more than I wanted: 460 ADU, 3.83 ADU/s
So based off that, it seems like I need a signal to be about 50 ADU above the background to find it easy to bring out. I know there's people that are a lot better at that than I am, but I'm working with my own limits here. Doing some math that tells me that for this particular target I "should" have used subs about 334s long.
I mention this because all of the discussion I ever see about this is focused on SNR but I think there's another factor to consider and that's how capable are you of pulling that data out of the noise floor.
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