I found this link I read ages ago and was wanting to find it again.
Its interesting to see the development of DSLRs sensors with increasing QE and lower read noise as later models come out.
One of the best is the Toshiba sensor in the Nikon D5200, that is really high QE and really low read noise. No wonder Nikon chose that sensor over the Sony equivalent.
Of the Canon's 1DX, 6D and 5D3 are the best with the 6D seeming to be the best performance for buck for astro and low light. Not 100% sure how this performance translates over to RAW images as these may all be for jpeg. If you look at dpreview ISO comparison tools jpegs of many cameras are often way cleaner than their RAWs due to in camera noise reduction processing. Usually at a cost of detail and sharpness as most noise reduction involves blurring.
http://www.sensorgen.info/
Greg.