The 500 f/4 is killer on the D4 with and without the 1.4 TC. It even crops well for the small birds. I find that the 1.4 TC gives me less than 5% image quality degradation, while the 2.0 is in the 15% range, which to me (overly picky as well) is too high of a cost. I shoot both the 500 and 300 f/2.8 VII with the 1.4 (I own 2) on the D4 and D3s and its a great combo for birds. For large mammals, I carry the 500 and the 200-400, as the zoom can be invaluable from a vehicle or when you can't move. For sports, well it depends on the sport and how much of the field/course that you want to capture from where you expect to be positioned. The 500 is way too much for hockey & basketball. Again this is where I reach for the 200-400.