I have no angst over the D600, own it and the D800, and am not inclined to check out the Canon 5D for myself, though I've shot with my brother's on occasion. The shutter issue is unfortunate, and I expect mine to be back from Nikon next week with a new shutter mechanism.
My upgrade to the D600 was in an interest for better IQ and I get that in spades over my old D7000. From what I've seen of the D7100 it has superior IQ to the D7000, but I doubt it will approach the D600, and no question that it won't be able to touch it for low light noise. There's a good article on the D600 vs. D800 by Scott Kelby linked elsewhere on this forum this morning and it does a great job comparing the two, along with measuring them against the D700. His take, unless you have the need for the large images that the D800 will give you, the D600 is the better FX camera for the average non-pro, and will give you quality superior to the D700. Give it a read. I shoot a lot of wildlife and cropping birds in flight is a given, so while I'm not always looking for big images, knowing that I can still get the MP's I need for decent enlargements while also cropping is a factor.