Real world difference:

(Shot using compressed Raw files, so spatial Raw compression artefacts will be visible in places)

When comparing against the Nikon D810, the differences between the two cameras are subtle: even in this challenging, high dynamic range scene, there was little, visible difference if the fully exposed-to-the-right shots. To illustrate a difference meant choosing a pair of images that had received 2EV less exposure than a perfectly exposed-to-the-right shot, showing that these small differences would only appear in a scene with even greater dynamic range than this one.

The difference between the Sony and the Canon EOS 5DS is much easier to illustrate. These shots were taken in slightly lower light, so could be given more exposure before clipping and hence are less noisy. Again these examples are 2EV below fully exposed-to-the-right examples, to make the differences more apparent. Even in this relatively challenging condition, the gap between the Sony and the Canon is not as dramatic as it has been in previous generations.

Shooting ISO Invariant using S-Log 2

On most cameras it's difficult to take advantage of their ISO Invariant nature because the camera's meter considers you to be hugely under-exposing and, even if your camera will present a preview that isn't related to exposure, the files you shoot are likely to appear almost totally black, making it very difficult to assess exposure.

Sony's S-Log 2 gamma curve: primarily designed for movie shooting, it ends up doubling as a handy way of making it easier to make use of the sensor's capabilities. The ways it does this are two-fold: firstly, because it offers an incredibly flat tone curve, the dark tones in the Raw file that you might want to make use of are pulled up and presented reasonably brightly.

Secondly, though, is the knock-on effect of this tone curve. Because ISO ratings are based on mid tones in JPEGs and the flat tone curve pulls its mid tones from a long way down the Raw file, the S-Log2 mode is considered to be a higher ISO than the normal tone curve. As a result, the lowest available ISO in S-Log2 mode is 800: not because the lower settings are being locked off but because an ISO 800 exposure is enough for a middle-grey object to be represented as a middle grey in the S-Log 2 JPEGs.

Looked at from a Raw perspective and what's happening is the camera is trying to use ISO 800 exposures but with much lower amplification than in standard mode, meaning highlights aren't being amplified out of the file. (If shot with the same exposure values, the ISO 800 Raw files from S-Log2 shooting appear to be somewhere between the ISO 125 and ISO 160 results in standard mode).

As a result, shooting in SLog-2 mode not only provides a more usable preview and output JPEG, it also essentially causes the camera to reduce exposure by 2.5EV to protect highlights.