Living in Botswana, let put across my experience. I used to use the 300 F2.8mk1 with a1.4X TC permanently fitted on my 7D. I was quite happy with the combo and as I was still learning to use my gear I did miss a few shots here and there. Last year during some major upgrades, I sold off the 300Mk1 and replaced it with the 200-400mm . My reasons
1) Versatility of the zoom for composition cannot be beaten !!!
2) I dont have to worry about weights and losing luggage enroute to places. I usually book a private safari and pay through my nose for having certain privileges such as being the only person with the guide on the "Bakkie"/ Open Safari vehicle.
3) The higher F stop is not too much of a problem for me.
4) Dust is a B***H, it gets in everywhere.
5) I usually holiday in private concession which means that we can go off road , where as in the parks you are restricted to the roads and will need a longer lens.
6) After two holidays with the 200-400, I am very happy and impressed with having it on a 1Dx !
PS: I am thinking of adding a 600mm with a crop body( 7D2?) and 1.4X TC for Birding !