Hi Mike,

It sounds like you know what you are getting into. You may want to see if prices for the 6D or a used 5DII drop to a level that you are comfortable with in the near future. If you are shooting primarily landscape and portrait I think you would benefit more from the full frame sensor and higher resolution versus the speed and AF benefits of the 1DIII.

The only other thing I'll add is that at current prices the 24-105 is an outstanding value.

Good luck.