7D and 1D pro level
60D and 5 D are mid level prosumer grade
Rebel and 6 D consumer level
7D is going to have pro level features above and beyond the 6 D, with the only draw back being a crop sensor. Then again the current 7D wasn't priced above $2k.
I'd say the 60D is far closer to a Rebel, and the 6D far closer to a 5D series camera - especially in build quality and the number of "consumer" features. The 6D is a surprisingly serious camera compared to the 60D, the AF may seem lacking in spec, but I'm finding it's a lot more usable than the 60D's especially for low light and tracking.
However, I think a better classification would be by photography type:
General pro-photography (weddings, random assignment work, etc.): 5D3
Sports/journalism/wildlife: 7D and 1D
Landscape and portraits: 6D
Easy to use (and "cheap") for casual photo enthusiasts: Rebel and 60D.
Then doesn't really matter what the price difference between the 6D and 7D is. If you shoot a lot of sports or wildlife, you get the 7D (or 1Dx if you can afford it). If you shoot a lot of landscape and portraits (where the FF sensor is important) you get the 6D. They become different camera's for different markets. The 7D mark II could have 10fps, be build like a tank, have a 40 point all cross type AF, and two Digic 5+ processors, and sell for around $2k just like the 6D. And people will just buy what works best for them. Much like what happened with the 5D2 and the current 7D.
I think the 5D3 is really a new class: namely the general purpose pro camera; mostly to satisfy the pro market that doesn't want to (or can't) pay for a 1Dx, and was finding the 5D2 (or 6D) too lacking.