I think the major thing (as a newbie to AP myself) we first miss is the reason we stretch in post processing. We are looking to get on screen on the camera what we want as the end product and forget we are grabbing all the subs to make up for the "lack" of what we see on a single frame.
I tried ISO 3200 and couldnt even get them to stack reliably (750D) but the single frames looked pretty good.
I took the leap of faith based on similar advice to the above and went to IS0800 (sweet spot for my sensor) and got the reverse, the camera screen showed faint smudges, but the subs stacked very well and a quick simple stretch got me far better end results.
If you want to have a practice at stretching without the hassle of capturing the subs go here and download a package of lights/darks/etc
http://www.rawastrodata.com/
After looking at the lights I started to understand what I should see on the cam screen vs what I thought I should see.
