I have stretched the image. Apollo, do you mean I should shoot M31 at 30 secs and what ISO level do you suggest?
Here are my latest two images:
M31 40 x 25s ISO 800.
M31 30 x 50s ISO 800
The latest version with 167 x 60s ISO 1600 is no better than this, even worse in fact!
(My handle is SilverLitz; Apollo is CN's classification based on how many posts I have made.)
The 25s bracket looks quite a bit better than the 50s set, even though this is not fair as the 25s set has only 1000s of total integration vs. 1500s on the 50s set. The shorter exposures do not blow out the core as much and have much better color.
I am not specific regarding 25s vs 30s, as your specifics are determined by YOUR skies, camera, scope etc... But I think you get the idea, not all targets need the same exposure lengths, and M31 and M42 need shorter exposures than most DSOs.
With your Canon Rebel (?), ISO 800 is recommended, as it is the ISO Invariant setting for Rebels or 80D. Canon 7Dmk2, 60D/70D, and 5Dmk4 the recommended setting is ISO 1600.
Make your life much easier by selecting just a few exposure lengths and a single ISO setting. I normally only exposure in full stop increments, such as 15s, 30s, 60s, 120s, 240s. You will need a dark library for EVERY combination of exposure and ISO, as well as sensor temperature. Getting a temperature matched dark library for non-cooled/regulated cameras is a major PITA; limit the number of combinations!
You need many more subs however for good images, MUCH more than you expect. SNR doubles for each 4x increase in total integration time. My 1st attempt at M31 last year had 346min of total exposures, shot with a Canon 70-200mm f/2.8L lens (at 200mm and f/2.8), using my ASI183mm-Pro at Unity gain and LRGB filters plus more exposures using Ha filter (to enhance the red star forming knots). This was from my Bortle 5+ backyard. Worse skies (higher Bortle) or slower scope (higher f/) require more time.