I'd view the ones on the DPR website, they were carefully made. Basically, you can use a lot of NR at those high ISO settings and have a small image look pretty good. When you look closely, much of the fine detail is gone.
Here is one I took at 51200 in extreme low light. It looks fairly good in the small size here, but much of the fine detail is gone. I did not bother with higher ISO, I would not use it this high unless it was a emergency.
Here is another at 51200