For example noise performance at ISO6400:
http://www.dpreview.com/reviews/stud...41.acr&x=0&y=0
Fuji XE1 with its X trans colour filter array has a handle on colour noise right up there with 6D which is also probably the current lowest noise camera. The 6D seems to have a bit more luminance noise than chroma noise.
Also 6D jpegs are probably the cleanest so the 6D jpeg engine may be realyl good for astrophotography. I know it sounds like sacrilege but if you set your white balance correctly there is not as much advantage to RAW if the noise is higher than jpeg.
So cleanest seems to be Fuji XE1 and Canon 6D, next would be 5D3 and the Nikons D600 and D800/E. The APS Canons are a tad noisier but still very good and 1100D seems best of that group.
None of this though, takes into account amp glow which is another issue to consider. As well as software support (Canon is king there, Nikon 2nd).
Another consideration to evaluate is well depth and QE. The Nikon D600 and Canon 6D are among the best there in both QE and well depth. The D800 has high QE but smaller wells. 5D3 has reasonable QE (a fair bit lower than these others at 39% versus 57%, 53% and 50%) and similar well depth.
Most cameras on review sites are evaluated on other criteria than astro performance hence a thread that can discuss this.
Greg.