6D + Canon 50/1.8 or D600 + Nikon 50/1.8? Help me decide.

I am trying to decide between these two options. 50mm is my favorite, and almost only, focal length. The f/1.4 options for each system seem a little soft to me at f/1.4 and softer than the cheaper 1.8 lenses at f/1.8. I like the rendering of the 50mm 1.2L and would keep it as an option in the future, if I went with Canon, but for now, it's a little too big and heavy for something I want to carry with me all the time.

Here are the pros of each setup, as I see things from having used the D600 and (briefly) the 6D and read about each online.

In favor of the 6D:

Silent Mode - This is the single deciding factor that would push me towards Canon. I find this feature to be absolutely incredible. The camera is quieter than my Leica!

Auto-Focus in low light - This appears to be really fast, better than any other camera on the market, even.

Experience with Canon - Not a huge plus in my thinking, but I did once use Canon SLRs in the past for a number of years. I sold all my lenses, but retain a familiarity with the system.

In favor of the D600:

Dynamic Range - This is the single deciding factor that would push me towards Nikon. By all accounts their sensors seem to be better for taking still images. (I'm not really interested in video.)

Nikon 50/1.8 - This seems like a slightly better built and definitely faster focusing lens under normal lighting circumstances when compared to the Canon 50/1.8.

What else should I be considering when trying to choose a small, light, full-frame, 50mm setup?

Thanks!