Imaging Resource compared the new GH5s vs the A7sII:
“At both 12,800 and 25,600, the GH5S looks slightly better than the A7S II at the same ISOs, which is both unexpected and subjectively highly impressive for a camera featuring a sensor that is a fraction the size of the other.
A sensor significantly smaller than the full-frame A7S II is beating that camera in low-light performance. I never thought I would see the day. With these test results, it’s hard to argue that the GH5S is not the new king of low light.”
Some more Panasonic GH5s vs Sony A7sII tests: