Get the 6D as a kit, try it for a while and then decide what the next move will be. If you decide to upgrade the midrange focal lengths you can always make a profit selling the 24-105. You might also consider getting the plastic fantastic, 50 f/1.8, (even cheaper used) with a 24-105 and 70-200. It won't add much to the cost and you get to decide how you like a 50mm prime before committing more to that focal length.
The 24-105 and 70-200 overlap, and for the overlap region, the 70-200 is better. That said, sometimes you just want to use one lens when going on a short jaunt and don't want to bring a larger or multiple lenses, so the 70-105 range is nice and is better than having nothing at all.
When I moved FF, I sold the 17-55 and replaced it with a 50 prime. So when I went anywhere, I found myself usually carrying at least two lenses: 16-35 and 50 or 50 and 70-200. It was a bit of a pain. The value of the 24-105 is its versatility; it'll lose the IQ battle to most other red rings.