<p>I went from the 5D, skipping the II and III, and went with the 6D.<br>
The 6D feels more responsive. I always felt the 5D took too much pressure and travel distance to trip the shutter. The 6D shutter release is lighter and more responsive. Auto ISO is nice to have over the 5Dc. However, Canon is brain dead in their lack of EV compensation capability when in Manual mode with auto iso.<br>
As far as image noise, higher ISO is much better than the 5Dc. 1600 on the 5D is very good. 6,400 on the 6D amazes me. The 6D is smaller and lighter enough than the 5D that it's appreciated.<br>
Wifi was not important to me in deciding between the 5DMK3 and the 6D. I've used it several times now for work. Bonus.<br /> Cannot think of a single thing I miss from the 5D going to the 6D.<br>
The quite shutter mode is a great new feature over the 5D.<br>
Except for higher ISO, from 1600 down image quality is the same. All the gains come from the experience of using the camera.</p>