Both Plays with light and myself use the 6D.
Speaking for myself the 6D suited my purpose too well that any IQ difference was not going to amount to the price difference.
A local husband and wiife photography team have both of these models.
They where originally both using 5D mk2's, he got a mk3 because they where moving into wedding photography plus he wanted the better ISO performance for his night landscapes.
More recently she got the 6D also for the ISO performance.
The reason I bring it up is they started a forum thread called "My 6D vs 5dmk3 impressions so far" which you can find here http://www.ausphotography.net.au/forum/ ... ons-so-far
Here is their website to give you a frame of reference of what they want from their image files. http://www.everlookphotography.com/