My problem is that you while you say you are planning to get the 6D, I read you doing little other than continually criticizing it.
In this case, you really might want to try to read again, I even often put a disclaimer under my posts to prevent just what you implied now. - I went out of my way writing about the 6d being a good camera over crop or 5d2, even topping the 5d3 in some things: http://www.canonrumors.com/forum/index.php?topic=11309.0
If you really want the camera, fine, then buy it. If you don't really want it, then buy another a different camera...and that's also fine.
Or if I simply want to wait some for the prices in Germany to drop (€100 in the last *week*, here it's still *more* expensive than the d600), that's also fine. While I'm doing that, I feel free to contribute to any threads here from people wondering about the same thing I wondered about, often pointing to my positive 6d fact list mentioned above. In fact, I'd feel free to post even if I'd decide never to buy a 6d because I'd think crop is sufficient for me and let other people know about my decision making process :-)
And, with all due respect, the implication that owner's bias trumps the experience they have through ownership is fallacious. If I own something that isn't actually good, I quickly sell it and replace it with something that is. It's that simple.
Without putting too fine a point on it, in my very humble opinion you are mistaken because there is no alternative to the 6d with Canon and in this price range except for the outdated 5d2. So what would someone who's unhappy with the 6d replace it with? Sell all glass and buy Nikon? Spend €1000 + 6d loss more and get a 5d3? See - it isn't that simple. Plus many people are simply attached to things once they bought it, I know I am.
As for what trumps what - I'd take my privilege to evaluate this on a case by case basis. In your case, experience certainly trumps owner's bias (if there is any at all). In other cases where someone does low light photography, then reads about lacking servo af performance, goes outside, snaps something and posts the (one?) keeper saying "it's just fine" I'm not so sure.