Following up my trials on relativ short exposures of deep space objects,
this is another intermediate result :

All in all my feeling is I should increase from now 10sec to 20sec, in order to get
very dim objects, like NGC464, out of the noise.

short exposures advantages are clear :
- forgiving of guiding errors, cleanup of bad seeing conditions or satellite crossings
typically 10% subs in total
- possibility for ALT/AZ mounts to image deep space objects : Dobson telescopes etc.
the disadvantage :
- at least for my camera setup, it takes 10 sec for exposure and 10 sec. for download
of one image. So in fact doubling the telescope time.
and not to forget we need at least 50% of dark images : very important for short exposures!
flats didn't really help
- not to forget vast amount of disk space required