While visiting the Woodland hide at an organised Northshots weekend in Scotland I decided to have a bit of fun with the Canon 1DX high ISO capabilities. Now, I was already very familiar with the 1DX's ability on high ISO as I regularly shoot at ISO4000 at football matches. Still it's always fun to push the limits and I have to admit that I was very impressed with an ISO 20,000 shot (yes that is twenty thousand ISO) ...
Yes, there is noise Mr Pixel Peeker, but in situations when you want to shoot a record shot and the light is very bad, then this will be very useful indeed.
And of course with a program such as Lightroom you can clean this up a bit to make it more presentable. Arguably even more than a standard record shot.
Below a 100% zoom/crop of the unedited 20k ISO image.