I thought I'd have a bit of a look at the difference between images taken on successive nights at the same ISO (800), exposure (5 min) and very similar temperature (12-13deg) and compare In Camera Noise Reduction and using no darks at all. The results are impressive. These are zoomed in screen captures of the final processed tiffs, number 1 - no darks, number 2 - ICNR. (and yes I know the stars look different.
) Neither has had any sort of after camera noise reduction applied.