first of all sorry for my poor English... I have been a Nikon user (D700) for a while (six months, four years ago) before switching to Canon and still very happy about my decision. I have a 5d MKII and a 5d MK III and I would NEVER change to Nikon (even if I would get a D800 for free).
The reasons are many... I would not hurt anyone but I would like to say something to explain my position:
1) Canon glasses >> I have six L lenses.. not possible to compare even with the greatest Nikon glasses..
2) Canon colours >> I am very surprised that nobody speaks about it
Have you ever worked on a greenish Nikon RAW? Have you ever tried to put good colors in a Nikon RAW file (similar to the great Kodachrome)? I know PS can do great things but I have never been able to get good results... with Canon it keep me two minutes to get exactly what I want!
3) Canon Services > Have you ever called a Nikon Service for a problem? Good luck!
4) Would you spend your time choosing one of the 345 AF points instead of understand the right focal plane to focus with a single point?
5) Have you ever tried both systems? I did.. I also used for a weekend the D800 and I don't like at what I get, it doesn't matter DR and many many MP... the images look VERY artificial..
So please TRY the 6D before judging... when I bought the 5d mk III I just saw the specs and I was sure it was only a real small update.. I change my idea when I started to use it.. USE IT AND JUDGE IT!!!