I will throw in my $.02.
On 200-400 vs 400 2.8, a lot depends on where/when you shoot. I shoot a lot of high school football. Around here, that is all at night on some terribly lit fields. For the me choice is simple. The 400 2.8. I am already at ISO 6400/8000 or higher to maintain 1/800-1/1000 shutter speeds on the fields I shoot. Can't afford to give up another stop.
If all I shot was during the daytime, the 200-400 would quite likely have been my choice. Had a chance to play with one for a bit. No doubt it is an outstanding lens. The versatility/convenience/IQ is amazing with the built in 1.4x.
Regardless of which lens you choose, I would strongly recommend setting aside some money for a couple new bodies. If you want to shoot sports, grab some combination of 1d4, 1dx, 5d3 bodies. Two bodies is the usual minimum for sports work. I often use 3 bodies.
Not that you can't do a good job and make nice pictures with 7D's or 70D's, but you stated you wanted the ultimate combo and that is what the 1D bodies are designed for.
I am not an SI staff photog, so take all this for whatever you think it's worth.
In the end it is your decision. The nice thing about high end glass like this, is it holds its value pretty well. So if you change your mind, you could probably swap a 200-400 for 400 2.8 with little difference in $$.