I LOOKED AT SOME OF THE I-R full-size test images: ISO 3,200 looks quite good, and 6,400 looks usable for news work. 12k and 25k would work in dire situations for some uses. The comparison with the Nikon D500 shows the Pentax is **MUCH** better at 812K ISO than the D500 is at ISO 812K, yet both are what I would call unusable for pictorial purposes. However, the fact is the Pentax has color differentiation,and some coarse details visible at 812k, but the images still look awful, whereas the Nikon is a big mass of pink-hued noise, and is well beyond "awful", and is in the downright atrocious category. Still...the Pentax KP is way better than the D500 is at this uber-ISO setting.
The difference at the highest, highest ISO setting is interesting. Is 812k "usable" in the Pentax KP? Maybe, for something like nightime police surveillance photos. Is the Nikon usable at 812k? No, not at all. Clearly garbage. Is the Pentax usable at 812k? Well...maybe for suveillance or game camera type images.
We're moving into new territory here.