I know nothing of the D600. But I know about the D800E.
IMO, if you can still swap them, maybe you should at least try to cancel or put your order on hold to give you some more time to consider… No 2k$ or 3k$ should go over the counter without feeling good about it.
If you can delay the purchase, there are people here that can help you make the right decision for your need and ambition in photography.
Again, if you can delay the purchase… you should have a good feeling about it.