...I looked at both the 6D and 5D Mark III and have chosen quality over cost for a couple of reasons which I think will be important for your consideration...
...The existing 7D isn't enough and the 6D is a downgrade (in part) for the reasons above. That has left me with the 5D Mark III, which in every which way you look is a pretty amazing upgrade (but at a cost)...
Jd
You make some good points JD, and trust me, I've gone back and forth MANY times over the past 8 months. Since I'm living in South America right now, I've needed to wait till I return to the U.S. to pull the trigger. If I were still stateside, I would've made a decision long ago! =)
But I agree - compared to the 40D, the 6D is a downgrade in the two key areas that you mentioned (FPS & AF). And that had me hung up for a while. I feel like I can live with the slightly lower FPS - 4.5 vs. 6 is close enough for my purposes. But AF has been the sticking point for me, hence my original question. If it's similar to or better than the 40D, then that would be ok with me. I know on paper, it's not...except for the -3EV center point, but it sounds like it does pretty well in real life.
To be honest though, the other major sticking point for me is price. In nearly every way that counts, the 5DIII is the better camera, but I've been increasingly frustrated with Canon's pricing structure. As of right now, the 5DIII kit is $4099 at B&H. The 6D kit is $2599. If the difference were $500, it's a no-brainer, I'd be getting the 5DIII. If the difference were $1000, I'd be on the fence, but might still end up justifying the 5DIII. But a $1500 difference?!? It's not THAT much better. I can get a new L lens, a grip and other accessories for the price difference and I'm starting to believe those items will have more of an impact on my photography than the extra features of the 5DIII. Everyone has different priorities though...
I should also note that I don't intend to upgrade for a long time after this, but I suspect that I would be tempted to if I chose the 6D.
Even with all my reasoning so far, this one still gives me pause. I will likely outgrow the 6D faster than the 5DIII. And, I can see the 5DIII holding it's value better than the 6D. So, does that make it worth the extra cash? Not sure.