I would hestitate to recommend equipment in a general sense, as a lot depends on shooting style - as you happy using a longer tele-photo lens?
There more variables behind what equipment than you first consider. My initial reaction is to ask the following questions:
1) Where in Africa are you planning on visiting? The terrain and your ability to off-road will affect how useful each lens becomes.
When I take my groups to Botswana or go individually, we visit the private reserves. We do not need to stay on the roads, meaning you can keep repositioning yourself so your 500mm is a perfect length.
2) Would you be having your own private vechicle, sharing with other photographers or in a shared game drive;
- In a shared vehicle, where people have P &S etc, the guides will try to get you as close as possible, meaning longer lenses are only useful for close up crop. Vehicle shake can also be a major issue. (You are better off with a zoom than fixed prime)
- when sharing with other photographers, it is a good idea to take similar setups, this way there are no arguments.
- Private vehicle, great. Move around how you want - though being restricted to roads as in Point 1 is a major consideration.
On a personal note, I think that if you did not have at least a 500mm setup, you will be missing reach, especially for birding.
In my experience, I would avoid using teleconverters, so something like the 80-400 that Nikon have would provide excellent versatility and reach, though maybe not the best image quality.
(The 200-400 & 70-200 is the best safari setup IMO, though I dont want to break the bank)
I have probably spent close to 15 months on safari in Africa over the last five years, and have found there will also be a situation where you wanted a different lens.
I run a blog that may be of interest you
http://www.thesafariphotographer.com
PS Lens support is critical, as you will spend a lot of time photograpinh in low light. Bean bags are the most the most flexible and cheapest option - with more fixed options running into $$$$$$$$$