5D3 vs 6D

The button layout is quite different - the 6D layout is more similar to the 60D. If you want to change flash exposure compensation or white balance you need to use the Quick menu and there is no thumb joystick. I'm not sure how annoying this would be. I found the 6D quite a bit smaller and lighter than the 5D III (had a short try with it yesterday) but still comfortable to hold. The shutter lag seemed the same as the 7D I normally use (i.e. near instant).

Also the 6D doesn't have a headphone input if video is important (not for me). One thing I really liked (coming from 7D) when reviewing images is the magnify button which zooms the view to 100% on the selected AF point - heaven. And it only has single axis electronic level (fine for me).

Oh and yes, it looked like the viewfinders were the same size and brightness so very nice indeed.