5dmkIII and 7D for football
I've used the 5DIII for two night games under OK High School lights with a 70-200 2.8. In one game I used single point and the other I expanded to 9. Focus point expansion gave me more keepers.
I'd be inclined to put the 400 on the 7D for reach and the 70-200 on the 5D for when the action is closer and you need a wider angle. My favorite spot is at the back of the end zone about 5 yards in from the corner...you get those fade routes and sweeps coming right at you and the 400 gives you no chance. Sometimes even 70mm is too tight...especially for sideline pics, so I use a 24-70mm....but that's more because I don't have the 400mm...I wish I did!!!