I just did the same thing(almost). I just purchased a 1D Mark III refurbished. It hasn't arrived yet, I can't wait. I bought it to replace my 30D, to be my fast action body(I have a 5DC too). The Mark III thread on this site heavily influenced my decision to buy this body, I was very very impressed by the images posted there. The body being a couple of years old, I am still blown away by the photos that body takes.
I plan on keeping my 5DC until the Mark III proves itself. I may look into a 1Ds Mark III to replace my 5DC too. I have a feeling I just might fall in love with the AF and handling of this body. Sorry I don't have any tips for you yet. Congrats on the new body though!
Rule books are paper they will not cushion a sudden meeting of stone and metal -ekg-