6D acceptable ISO setting

Some of my nighttime footage has quite a high ISO, and seems to be acceptable. But for bright style people shots, what would be the highest acceptable ISO levels? I'm finding my lighting kit is not as bright as I'd like in some settings.

I use ISO160 on my Canon 5D MKii in the studio and have studio lights to raise the light level but I also have lenses with apertures of f1.4 and f2.8 to give me shallow depth of field and also allow lower ISO settings. I would use up to ISO 1600 max with the 5D2 for night shots.

Easy way to tell. Look at the footage or photo at 100%, is there grain, noise or globs in the dark or shadows? If so you've pushed it too far. Some times an ISO of 300 is too much. Really depends on subject and lighting. With my Canon 7D I never push the ISO, if I can't get the shot with under 300 I pull out the 5D MK III.

Just for thought, (since iso can be a complex thing to discuss in a forum) there are occasions where a 3200 iso can yield a cleaner image than 1600 or even 800.Depends on how you expose.Try always to expose to the right,even if artistic purposes dictate low key (still exposing to the right does not contradict artistic intent) .
The key is to expose in a manner that you will bring down noise levels in post (crush mids and blacks instead of pulling them up)
6D is even better that the mark III at low light and has cleaner iso, so depending on what you are shooting you might as well easily go to 6400.
Now if you need to light a model and find that your lighting kit isn't enough going to 3200 could certainly expose the talent but it's still bad practice and also means that you dont have the means to light a person properly so iso and exposure is the least of your concerns at this point.
And bear in mind that when you go to higher isos in canon cameras you lose highlight detail in favour of blacks.
So the lower the iso you can be that is right for exposing the subject without losing detail and without bringing up noise the better (that's why i said in the beginning that it is a bit complex) .
Ans since we are on it and i feel rather chatty today please use only the real iso's in canon dslr's (100,200,400,1600,3200,6400 and 12800 and beyond if theyre true analog iso's and not digital) .
I think 6D's 12800 is real analog iso, mark III is 6400, and mark II 3200, but i may be wrong on the II.

Great. Thanks for advice.