Ok, so I bought the Canon 1D Mark III! I have done two photo sessions so far, and I've gotta say that I love it. I came from a Canon 70D. Yes, the 1D III is an 11 year old camera, and yes the controls are a lot different than coming from a new age standard DSLR. If you understand exposure, and understand the exposure triangle and how to manipulate the camera to meet your needs, than any camera system, new or old, can be great for you. The 1D produces a look on the images that I love, I have changed the ccontrols around a little to meet my needs, and so far it has produced beautiful images! I do enjoy the heavier camera, and the built in battery grip. I makes life easier, especially on wedding days! Yes the weight can get to you, but that's the name of the game with this camera.
If you have any questions at all about my usage with the camera body, or my experience at all, don't be afraid to write me and let me know!