I owned a 40D and a 5DII, now i have the 5DIII.
The 5DIII is the 40D speed + 5DII IQ combined + a whole lot of extras. It's worth the the $.
The 6D is lower build quality, poor ergonomics compared to 40D, and much worse than 5DIII
Get the 5DIII, and enjoy the full-frame goodness
I think you have 6D mixed with the 60D.
To OP. I recently had the same question, and went with the 6D. I don't regret it one bit. I am not a professional, and I don't shoot sports nor wildlife. The 6D AF is more than adequate, seriously.
I just want to advise you that don't feel like its not good enough. It's a great camera. I don't think the 5D MIII is worth the $1000 that you can put in lens or accessories. But that's my opinion.
It really comes down to whether you NEED the AF of the MIII. If not the 6D is more than practical. I love it. Honestly think about what your needs are. The 6D will still be around just as long as the MIII. So don't get thrown off by that comment.