This could easily become a Canon vs Nikon thread and that would result in a long list of people venting their views.
D600/610 vs 6D comes down simply to which tool suits the user in my opinion.
I have used both Nikon and Canon (current models) and whilst I think the D600 is a very fine camera, I was always envious of the Canon lens range. I didn't find the various Nikon zooms to my taste but loved the 135/2.
Having recently changed from Nikon to Canon, I have to say that I do not have any regrets (none at all) as I have found the Canon cameras and lenses entirely suit my purposes and give me the pictures I want.
I'm not saying that one system is better than another, but that Canon suits me (and many others) better.
At the end of the day, either camera will be more than capable of demanding use and will produce (hopefully) award winning images for the user.
The o.p. refers to RAW use in terms of IQ and DR. The Nikon has superior DR but this may not necessarily be the most important factor for every photographer as higher DR can lead to a flatter look to a picture, particularly portraits.
As far as IQ is concerned, bearing in mind that the term IQ can cover many things, each of which will be more or less important to any one person, I think the overall IQ is better with the Canon. In my experience, my pictures are sharper wide open (possibly more to do with the lenses than the actual sharpness captures by the camera), the colour are more to my liking (very subjective - I know), exposure is more often correct and the way the Canons work in low light is more pleasing to me.
A lot can be done in post-production I know but the long and the short of it is that whereas both cameras are fine tools, it's the lenses that may well swing it for you. In my case, the Canon lenses were what I wanted and the Nikon ones weren't.