Had an extended 'play' with 6D belonging to a friend. Quite petite and light ( the camera) battery grip would be helpful for bigger hands. Aspect ratio of the screen variable, interesting, not sure vital. Quick look at a few images at various ISO's looked fine. Canon seem to be going towards the Toyota of the camera world, works well, pretty reliable, not risky or over ambitious, maybe what you want in a camera. 20Mp plenty enough IMHO , sometimes wonder how many 800E's only have images posted on web? Seems like a pretty good camera.
You can use the joystick-type thing in the middle of the main control dial on the back but it's not very precise, certainly selecting diagonal focus points is a bitch.
Another gripe is the sync speed of 1/160th which is somewhat restrictive. Use this camera with cheap triggers and cheap flash and you may have to go down to stupidly low shutter speeds to sync correctly (I had to do this a couple of weeks ago using old Bowens heads and cheap Yongnuo triggers, as a result the modelling lamps were partially visible in the results)
The built-in WIFI is superb if you have an iPad. I was shooting some promo images for a tattoo artist friend of mine the other day and they were loving seeing the instant feedback in the iPad display.