Why should I own a 70-200 F2.8 VR?

I would recommend the 300/f4 approach and then add the TC-14EII. That gives you the equavalent of a 630/f5.6. The high ISO performance of the modern DX cameras make up for the one stop in aperture (compared to the 600/4).

I've gone down this path myself to tide me over until I can afford the 600/4 for my D800E