Here are a couple of examples:
http://www.cloudynights.com/uploads/monthly_06_2015/post-205769-0-45448000-1435261812.jpg
http://www.cloudynights.com/uploads/monthly_06_2015/post-205769-0-36074400-1435261831.jpg
The top is the A7s, bottom is 6D. The A7s is 42 minutes of exposure at ISO 1600. The 6D is 60 minutes of exposure at ISO 1600. The 6D subs were gathered under darker skies, by about a factor of 1.6x, which is 1 2/3rds stops BETTER than the skies the A7s subs were gathered under. The 6D was modded with a "full spectrum" mod, which totally opens the sensor up to as much light as possible by entirely removing all the filters. The A7s was only a partial mod, which removed the primary IR cutoff filter, but left all the other filters in place, so there was still some filtering occurring.
This scenario gave EVERY advantage possible to the 6D. The 6D has longer integration time by 43% (half a stop). The 6D was a full spectrum mod so it had no filtering of any kind, whereas with default filtering it doesn't even get 20% of the primary Hydrogen emission, Ha (hydrogen alpha) while the A7s still had it's first LPF filter in place which filteres out some Ha. The 6D was used under darker skies (nearly a pristine dark site, 21.2 mag/sq"), which reduces extra unwanted light signal, which reduces photon shot noise, whereas the A7s was used under skies that had a moderate amount of light pollution (20.0 mag/sq").
This all gives the 6D at least a two stop, if not a two and a half stop, advantage...and DESPITE all those advantages over the A7s...the A7s still produced a cleaner image, with more stars, with better colors, less background noise, and a deeper exposure.
Don't know about anyone else, but that is pretty telling to me. The technology Sony is packing into their cameras, whether all the external factors are perfect or not (lot of people on this forum bring up Sony's plastic mount as a major issue, for example), is truly phenomenal stuff.