Those look pretty good - I might have to try Centaurus A myself I think. What Gain/Offset are you using?
If you haven't seen it, you might like to read Ray's thread:
http://www.iceinspace.com.au/forum/s...d.php?t=155908 on exposure times for the ASI1600. It might not be necessary to try for longer exposures, but perhaps more of them?