Run&Gun
Veteran
When Canon released the C300, they said at ISO 12800 it had the same noise as 35mm film, which is fine by me. I'm sure the C300 was applying ample noise reduction at that point, though.
In the tests by Tim Daust, the cameras looked fine to me up to 12800, probably cleaner than 35mm film. It's hard to tell through Youtube compression, though.
DISCLAIMER: I don't do this anymore for a living and am not worried about pleasing clients, some of whom may be allergic to the slightest speck.
When I got my original C300, I remember thinking how ridiculously clean ISO 6400 was, considering it was ISO 6400. Kicks my F55 in the balls, even today, in low-light. Over ISO 3200 on the 55 and it can be a mess.