Thoughts on the IR results...
At base ISO: Impressive levels of detail - even against Pentax, the 5DS is holding its own (but of course, at 35mm there's really no competing with the larger sensor size of MF).
At high ISO: the 5DS seems about on par with the 7D2 when viewed at 100%, maybe even slightly worse - however, when you downsize the 5DS file to 20MP, the 5DS wins out. Against the 5D3, the 5DS seems about one stop worse in high ISO (but pulls out significantly more detail, which may make up for some or all the difference for some shooters). And against the D810, the D810 image is a bit cleaner - but the 5DS seems to produce a finer grain which may clean up nicer in post...
- Took a look at all the studio files throughout the ISO range...good detail retention up to 800...at 1600 there is noticeable degradation...and by 3200 you've lost most, if not all, of the fine details. At 6400 I actually didn't notice much additional detail loss, but of course there is more noise (grain). Not bad by itself, but for a FF sensor it's definitely a step backward. Downsize the 50MP files down to the 5D3's 22MP and you still get more noise, but you also get a sharper overall image.