Bill makes some great points in his post. I totally agree with what he said and really like the research he did on the moire issue. That was very helpful.
Like Bill said, the big thing you'll have to determine is how important a full frame sensor is to you. Basically, is it important enough to spend another $900 on a camera body?
Personally, I like full frame cameras because I know exactly what field of view I'm going to get with every lens and because it makes getting wide shots a heck of a lot easier. Otherwise, you may be forced to buy a super wide angle lens (like a 14mm lens) in order to get the effects of a wide shot in a cramped situation. However, you'll still have to determine how important wide shots are for you to see if it's worth the extra mone (and it's quite a bit extra at that). The specs show both cameras to be very similar besides the size of the sensor.
If I were to buy a full frame sensor camera from Nikon, I would go with the D600. I've shot with that camera before and I was really impressed with it's image quality, responsiveness, and ease of use.
Hope that helps!