Kyle, take the 200-400, with the proviso that the new 100-400 won't be available by then.......I travel a lot and if you are vehicle based it's great, my kit for vehicle base travel is the 200-400 on a 1 Dx, and the 70-200 mk2 2.8 on another 1 Dx...I'm fortunate to be able to borrow the 2-400, so don't have the outlay to bother about!!
If I look at the shots I took, the great majority were with the 2-400, and quite a lot had the 1.4 in as well, and I also added an extra 1.4 on occasions when I needed really long reach...in the Serengeti for instance you have to stick to the roads so you may be shooting from a greater distance.
I'm off to Brazil, the Pantanal, in a couple of months and there I'll be taking a 300 2.8 mk2 with 1.4 and 2x mk 3 extenders, probably have it mounted with the 1.4 as standard, as for an old codger like me the weight of the 2-400 for general use is just prohibitive.
The low light capabilities of the 1 Dx are so good that I wouldn't bother about f4, I use manual set up and auto iso and check histogram frequently as I often use exposure compensation...as much as +1.6 stops on occasion.
I suspect when the new 100-400 comes out, sales of the 2-400 will drop, I know Nikon user pals of mine have virtually stopped using their 2-400 f4 lenses in favour of the new 80-400 lens they have, which is getting a formidable reputation, and it's light as well.
Just remember, a lot of people make (in my opinion) a basic mistake by shooting out of the top of vehicles, I much prefer shooting as low as possible as I think it gives a more dramatic perspective.
Lastly, enjoy the wildlife, don't spend the whole time looking at it through a viewfinder!!