In the beginning, I was scared to go above 500 ISO but 500 ISO is actually noisier than 1600 ISO. You have to the give this sensor light. If you don’t give the sensor enough light, then your 8 bit colour space will go down to 6 bit then 4 and then 2 bit colour space at which point you have no control in post, it is better to feed it a little more light and then adjust your colour and contrast in post.
(DSLR CInema: Crafting the Film Look With Video – Kurt lanchester – page 48)
*DEALING WITH ISO ON A CANON 5D MARK II*