I'm a 5DC owner along with a 24-105 and a 50 1.4. I have been wanting better AF and AFMA for a long time now and never wanted the 5DII because of the AF.
I would love a 5DIII, but I believe it is a 2800 dollar camera that after a year of being on the market should be 2500 dollars. I would have preordered for 2800. The new 24-70 lens is very very expensive and this was my main choice for a single travel lens.
After seeing the comparisons between the 5DIII and the D800 I think that the D800 is much more of an improvement in sensor performance over the D700 than the 5DIII is over the 5DII.
From the rumored specs, I think most people agree that the D600 looks better on paper than this new Canon FF camera, especially after the improvements shown in the D800(mentioned above.)
I love Canon, and have been a loyal customer for years, but I am not heavily invested in the system. I don't like the direction of their pricing(one of the reasons I bought them in the first place was the relatively cheaper pricing than the Nikon version(Canon 24-70 I is cheaper than Nikon 5DII was cheaper than D700.) That is not the case anymore.
If Canon makes a FF mirrorless, I will be thrilled and buy it if it is around $3k with a lens.
However, at this moment, comparing a D600 for 1500 and a Canon FF, I will choose the D600. I wish this was not the case, but in my opinion(and based on rumored specs, and sensor performance of their current cameras), the Canon offering is a little low on features, low on sensor performance, and higher in price. I will gladly purchase a D600 and 24-70 for around 3300 dollars than the Canon versions for over 4300 dollars.
My .02 cents.