Previously in another thread, I've raised the possibility that 6D is built on an entirely new generation of sensor.
Definitely not, this was already ack'ed by Canon - it's the same sensor tech, though the 6d has a bit little larger pixels for the loss in resolution. The reason probably is that after the criticism about the lack of advancement 5d2->5d3 Canon had a 3/4 year time to optimize everything else.
The 6D shots might be a little bit underexposed compared to 5D3 but nevertheless
If you look at the exif data, all 6d shots have a shorter exposure time then the 5d3...
but small differences in image parameters between a consumer and a pro camera.
However, this shows how desperate the Canon crowd is for sensor advancement ... the Nikon competition obviously has left its mark :-> ... and again, imho there is no fixed distinction between "pro" or not except for marketing, why not use the 6d if it is at least as good or even better (low light af) for some shots?