The Sony A7S series has always been considered the leader in low light at very high ISOs. But at just 12 megapixels, it’s a big sacrifice in resolution to get there especially in the 8K age.
The main thing that strikes me about the current 24 megapixel full frame sensors is they are CLEAN. Certainly ISO 3200 on my Panasonic S5 looks very similarly clean to ISO 3200 on the new Sony A7S III. I’ll be exploring this with my own test soon.