Better yet, pick up a lightly used 5Diii and wait until the 5DIV is tested, reviewed, firmware fixes, software updates, price drop etc all occur.
Really easy to say, but cash transactions in the $2000 area with a private individual are non-trivial.
There is of course risk in buying a used $2000, what happens if it does not perform as expected?
And of course, the risk of selling the camera. The value of the used 5Diii probably won't drop too much, but you never know.
We have no idea how well Canon is prepared for the launch as well. A lot of unknowns.
Which is why I am living with my 7D until I get my hands on a 5Div.