Yeah, I own an A7s and a Fs700. The A7s is one of those cameras you're referring to. 12MP sensor. When shooting slog2 the lowest it will go is 3200. If I expose correctly, middle grey at 32%, per Sony's suggestion, then the low amount of noise turns out quite nice.
The Fs700 is much different with a base iso of 680. I can usually live with the noise at 1250, but I don't like pushing it past that point. The noise from the Fs700 isn't as visually appealing, in my opinion, as the noise from the A7s sensor.