I've been using my 7D for a couple years, but have been dying to get a full frame for a while. I debated selling the 7D and getting a 5DIII, but decided to keep the 7D and pick up a 6D. I can use them both with my 24-105L and 70-300L lenses. I love the reach and speed of the 7D for birds/sports.Everyone has his/her own standard. So why not judge it for yourself. Shoot a series of photograph from ISO3200 and up. Load everything in your favorite software then see at which ISO you cannot tolerate the noise anymore. It's easy to do and you will not regret later "oh, I should have not listen to xxx." It's a great camera, congratulation and enjoy.
On my 7D I've used auto ISO with a maximum of 800. What would you suggest is a comparable maximum ISO for the 6D?