Ray, yeah the end-result noise is what we perceive in the end, but obviously doesn't factor in the noise introduced and/or reduced in processing which can't readily be reversed to reveal the SNR of the original linear, single sub or stack.
I figure there's going to need to be a baseline for a pre-processed image to ensure decent results. If, say, I stack only 4 subs, it's only good for a sneak peek and not worth processing (no doubt obvious!), but for a given target I'm going to want to figure out a rough number of subs to aim for.
And this is without even considering proportions of L to RGB
