I'm currently using a D2x and D300s and plan to add a D600 early next year. I'd like to know if the dx crop is good enough to do away is dx bodies? Is the crop similar to the D700's crop where the dx outline is a red rectangle displaying the area? Do I keep one of my dx bodies? I like dx for the extra reach, especially with the Sigma 150-500 OS but could have it both ways in one body.