Nikon D600 vs. Canon 6D in Low Light?

Buyer's remorse is understandable, especially factoring in the dust/debris on the sensor issue.  I like my D600 and I'm going to take a measured approach to sensor cleanings.  If I was a working pro shooting landscapes at smaller apertures, I might be a bit more annoyed.

Personally from the samples I've seen the 6D is very good at high ISO, and produces better high ISO JPGs.  Also, the 6D should do better at center point AF in very low light with its -3EV rating.  But I think there are a few caveats to this:

If you want/need to pull shadows, you might find the 6D doesn't do it as well (especially JPGs).  If you learn the camera's quirks for metering or are good at using manual settings, this may not apply.

If you shoot Raw, the difference between the two becomes much less.

If you feel strongly enough about this, rent the camera first.  I've learned I can look at samples all day, but to know what the files look like for things that I shoot....I need to shoot with it!  Also, you may find out aspects that aren't typically seen in carefully shot studio settings.  Things such as shooting under different color temp lighting, etc.  Or maybe just a particular handling issue or aspect you find great/annoying.

Finally, the more I read forums, the more things I find to "hand-wring" about.  Conversely, the more I go out and shoot, the more I like and understand the D600!