To me low light photography isn't about street, bar, sport and events, but family pictures at home with f5.6-f8.
After my 5Dc started to show its age and support was ended by Canon I switched to 5D MKII and never liked high ISO from it. Not even 1600, which was most used on 5Dc. Looked at 6D high ISO examples.... Don't know how to put it, but high ISO of modern cameras is missing something to have it crispy on portraits and more casual pictures of people.
Sold 5D MKII with no intention to upgrade, but later on received as gift the outdated CCD camera which isn't worth of mentioning on P.O.T.N.
. I have it set on ISO200 and 1/30-1/60, with old cheap lens from fifties set on f5.6 and on-camera flash. It gives sharp and crisp indoor portraits. Not like re-sized to 1K pixels for the internet, but 100% cropped ones on the screen.
I might pool out from the cabinet used to be famous GF lightsphere to smooth shadows 



