I like the idea of 2 5D3's. Right now I have one 5D3 and a 5D2. The problem is (being an amateur) I cannot justify a second 5D3.
My 5D2 has 15-20K clicks and I guess my 5D3 ~5K. (OK these numbers will increase alot during Summer...
So if I get a second 5D3 chances are it will be practically unused when 5D4 arrives!
The other reason may seem a little silly to you:
I was able to do the following using Magic Lantern with my 5D2:
Bracketing: 2 shots. Distance apart 5EV. 1st shot (with the longer duration) with timer delay.
I cannot do exactly the same with 5D3.
Yes, I can set the bracketing to 2 shots. But, the timer delay is an all or nothing.
I need the second shot to be up to -5EV and be shot immediately the 1st which needs at least the timer
as it will use slow shutter speed and telephoto.
Maybe you think all these are crazy but I was able to take a succession of 2 photos that I merged in one
showing a moonrise near an ancient temple. -5EV set the moon at comparable brightness (it was one day past full moon) and the succession (almost) without delay made the merge easier.
So maybe it seems silly but I may need again this 5D2/ML feature. Maybe when ML is 100% functioning on a latest firmware 5D3 I will think again.
Other than that I am crazy with my 5D3