Just had a short test with the 6D earlier. Really feels and handles like a full-frame 60D and looks like a 5D II mini!
Its feels light! Silent shutter's about the same as my 5D3, which is great for stealthy shots! I didn't really notice any AF issues in shop lighting, so that's good! Good thing the buttons are not as stiff and mushy like the 60D, but still not as nice as other DSLRs I've used.
All in all, a very decent no-frills FF camera. Straight forward and simple to use like the 60D. Great for any only center AF point loving folks. Better than the 5D2 imo.
Would I pick the 6D if I wanted a budget FF? Sadly no. I'd rather go for the D600, but that's just me.