The following is a short test from Andreas Peters:
“Back in 2015 I did an ISO comparison of the Sony A77II vs Sony A7II . As I now have a brand new Sony A99II I did the same test with this camera. All photos can be found in my Flickr Album “ISO test Sony A77II, A7II, A99II” https://flic.kr/s/aHsk9dazjD Remark:
For the Sony A99II I used the Tamron 70-700mm F2.8 Di LD (IF) as I do not own any F2.8 lens with a focal length of 55mm.
The Tamron 70-200mm @70mm gives a similar field of view for this test (I could have used my Sigma 24-105mm @55mm but this is a F4 lens which would have resulted in completely different exposure times)”