I don't actually know the answer to your question. My experience with image stacking is daytime landscape photography. I've found that stacking can greatly im

I don't actually know the answer to your question. My experience with image stacking is daytime landscape photography. I've found that stacking can greatly improve the shadow detail. The ETTR technique gives nice blue skies, and restrains other highlights, but naturally, with shorter exposure times, the darker portions of the scene get less exposure than they would if you allowed the skies to blow out. I'm only guessing, but there must be a minimum time for the exposure. Stacking won't change that. My assumption (and I'm not a statistician) is that the noise floor moves lower with stacking. Taking multiple images and stacking them is basically taking multiple samples. The random (Poisson shot noise) is averaged out across multiple images while the signal (the star) is a constant across the images. As you can see from the linked article, there's an amazing amount of detail that can be recovered from the shadows if you know how to get to it. In a dark sky environment, you'd be limited to the camera's sensitivity (the analog gain applied using the ISO setting), but in the city environment, almost certainly the sky light is the limiting factor. I have not experimented with custom cooling. Aside from some moon photos and photos of the recent partial (in my area) solar eclipse, I'll leave astrophotography to others.