I guess the right people will come along with enough expertise soon, until then:
I have used the K-1 for Milky Way images and have used ISO 1600 at f2.8 and 30secs to get a reasonable exposure. This has generated some star trails on the edge of the frame at 15mm and 21mm, so I've dropped that time to 10-15sec and ISO 3200 and can achieve similar results like this:
I was out two nights ago chasing the Milky Way again but trialing the astrotracer for which I dropped to ISO 400 & 800 for approx 4:30secs / 3omm and f2.8 to get an idea of what seems to work best with that feature. TBA on that one.
A good website to review settings for Milky Way photography is Royce Bair's:
Into The Night Photography his Flickr page is here:
https://www.flickr.com/photos/ironrodart/ You can see from his EXIF that he's at 25secs and ISO 6400 using the 5D Mk III and the Tamron 15-30. He has some very good information about camera settings on some of his Flickr images too.
Of course if you're talking different astro like deep space stuff this technique, as demonstrated on the Milky Way is the next approach I intend to try to address noise:
Video: Noise Reduction with Image Stacking – Lonely Speck
Something I'm finding too is that a lot of the noise I'm capturing can be controlled by sepcific techniques in PP, so if you're looking at trying this yourself I'd recommend pushing the ISO to 3200-6400 for a 10-15sec exposure at f2.8. In PP I use LR6, turn off the default sharpening then use some NR to taste. I return to the basic panel in LR6, or you could use the curves tool and work the highlight/shadow and blacks sliders to further reduce the noise. Note also that I don't use the dark frame subtraction. With the shorter exposures it's easier to try both and see which one you prefer.
Hopefully some of this info will be of assistance.
Tas