The OP is looking firstly for portraits and night scenes. The obvious advice is that 6D is world leader in low-light focussing. Still no-one seems to read the question and just gets on their hobby horse.
The high ISO/low light performance of 6D is also "dynamic range". It has opened my eyes already to new photo opportunities that I would not previously have dreamed of attempting.
oh well - if you're not blinded by the brand you might want to have a second thought on your claims ;-)
DXOmark.com tests the A7R much better at low ISO and more or less on par with the 6D at high ISO and the focussing seems to be quite impressive at low light too - if focussing is a problem at all - it is not for me on my 5D II
But don't necessarily trust my worlds - 9'15'' is the part you're probably want to see or of course the whole video from a PRO who makes his living with the camera and he seems to be enthusiastic about the possibilities
At low ISO there is no doubt that the Sony Sensor wins hands down. At higher ISOs the sensor is at least on par with the Canon sensor and the EVL viewfinder seems to work amazingly good - especially for the slow photography the OP inters to do.
Don't be overwhelmed by the marketing - it is time to add some further food for thought and not to be blindly following a brand.
DXO measures speak a clear language and I am sure within the coming weeks we will see more and more excellent reviews that bring more evidence on the image quality.
For high speed photography I'd be reluctant to buy any of the affordable Canon FF cameras since their farm rate per second is IMHO unacceptable for action photography - that's the reason why you see many 1Dx at sports events and almost no 5D III or 6D
I stand by it as a Canon shooter - if you want to get the utmost out of your precious Canon lenses buy an A7R and a metabones III Canon adapter and do what Canon should have done much earlier - if Canon brings out an equivalent sensor in a nice body you can still sell the A7R after some time and use the "original equipment" - until then you can outperform easily all current Canon bodies
I've done some shooting last weekend with a friend and he used his D800E and the 300 f/2.8 VR II vs my 5D II and the 300 f/2.8 L IS USM II - the Sony sensor in the Nikon with the 300 wins technically hands down at all ISOs we photographed - no doubt current
Canon DSLRs don't deliver the best image quality on the market as the OP clearly requested
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isn’t it funny, a ship that leaks from the top
ISO 9000 definition of quality: 'Degree to which a set of inherent characteristic fulfills requirements'
I am the classic “Windows by Day, Mac by Night user'
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