Although I personally shoot a 6D I don't think I would recommend jumping up to full frame if your main goal is documentary shooting. You only have one lens that would work with a full frame camera, and less depth of field isn't always a good thing(although it pains my soul to say that... I am an unashamed bokeh whore), especially during run and gun documentary shooting.
I have been using the eos M to supplement my 6D since December and I'm loving it. Having magic lantern on there makes it a little beast of a video camera. For the price I don't think you can beat the M+22 for a super compact camera. Just remember that its very light and you'll want to have it on a tripod/monopod most of the time to combat the camera shake induced by using such a lightweight body.