I guess you have to be clear on your purpose first.
Are you wanting to sell your photos - then clearly your needs are defined professionally.
On the other hand, if you are into it for the love of it, then more than equipment, familiarity with Game photography on-the-move, and practice and skills would be important. One can shoot beautiful pictures of most animals in a zoo, but shoots on safari are IMHO not just animal portraits. One is better of capturing the essence of capturing them in their own habitat. Technical perfection can be left behind.
Believe me no zoom lens is long enough, and no body capable enough to limit your own creativity and skill. As soon as you would get comfortable with 400mm, you would want 500, and then 600 ......same for bodies.
So go for what you are comfortable with. If you are beginner, then even a Super-zoom could provide you enough artillery to shoot all the wildlife you come across.
Nikon or Canon - dead heat, mix does not make sense
DSLR or Superzoom - limitation is photographer not equipment
300/400/500/600 - your comfort level
F2/f2.8/f4/f5.6 - budget constraint
That is my 2p worth of input to you.