Steve,

I want to read your pdf on how you train birds to pose in the air for you! Great pics!

The lens is more important than the camera in getting great shots. You are buying a great camera so get a great lens. I would stick with Nikon. My go to lens is the 24-70 VR (one of the holy trinity) as it covers so much of what most of us do--however you should select the best Nikon FX lens that best suits your work. You get what you pay for. For great advice call B&H and talk to one of their pro photography people.

I'll probably be trading up myself, from the D800 to the D850--but I haven't yet told my wife.

I agree with Ralph. Am recording NASA during the day and will shoot at the Chicago Botanic Garden that has several nice open fields, even though we will only get 87% coverage. However I am most interested in shooting the many other people around me who will be impacted in many different ways by the experience. Then when we return to South Carolina in late September my camera club friends can share their several pictures (they will get 100% coverage). As photographers we all have our interests and this is a great opportunity to fulfill many of these interests.

The weight issue is a concern for the flight to Africa, not the bush planes. The tour companies and bush planes all limit you to one bag per person plus carryon. The one bag is duffel bag size so you won't carry much clothing, but every camp I have been to has same day cleaning so three outfits plus a couple extra light shirts and is fine. Everyone looks the same every day and by the end of the trip you have worn the same outfit all day about half the time. Someone asked about batteries and battery chargers. Take a charger as you will have electricity available in your tent/cabin or at the main lodge.
And, yes, go to Africa and the Arctic. We've taken several great trips but the best have been two to Africa with A & K and one to the Arctic (between Eastern Canada and Greenland) and another to Alaska with Lindblad National Geographic. Both operators have wonderful guides and National Geographic incorporates wonderful photography into their trips.

I found whwiden's report to be very interesting and wonder why others need to be critical of efforts to be helpful. We have a wide range of photographers on this site and this is great for some. Others can do what I often do--ignore that particular input.
Regarding his recommendations, as someone who took a very comparable trip earlier this year and has been to Africa previously, I would heartily concur. I find that two bodies is a great idea as you can put a long lens on one and short on the other and keep shooting rather than change. I took two Nikons-D7000 & D800. I disagree with his comments regarding lenses. I have borrowed several long lenses but bought the Nikon 200-500 for Africa. It is not as heavy or big as their more professional lenses, but is 5.6 throughout and took very sharp pictures. I've had a couple of pro friends tell me they use it regularly now and would recommend any Nikon shooter look seriously at this lens. (No, I don't work for Nikon.)

Regarding lightyear's questions, don't take a tripod to Africa. You just cannot use it on any of the vehicles I have seen. Most vehicles have bars or ways to support a beanbag and I found them helpful. Most of the time you are shooting animals you will have time to get a stable position. The birds are also great and different--if you are a birder you already can handle a relatively long lens on a flying bird, just ask your driver to stay stopped while you shoot. If you aren't a birder you will be seduced by what you see there, so practice before you leave.
I think most all African safari trips expect to have serious photographer's among their groups. The guides are very knowledgeable and the drivers will get the vehicle in a good position. And the non serious point and shooters will understand and be patient (and jealous) of your commitment to getting good pictures. We have used (and recommended) A&K for our trips. They know Africa, are not the most high end company but offer great camps and guides, and they clearly understand the photographers that travel with them.

My wife and I were there in January--rainy season, which you will learn is not really the wettest period. That is caused by a flooding river. We did our flight during rain and it was wonderful (although the doors were not open so pictures were sometimes difficult). Used several lenses, but primarily f/2.8 24-70 as wide views capture the assume size of the falls. Took two hikes and did cross the bridge-one from Zambia entrance and one from Zimbabwe. I would recommend both if you are offered. Very different views. You are into dry season and hopefully will still get all the activity from the falls others have mentioned.

By the way, when you are in Botswana be prepared for a wonderful experience. I had two Nikon DSLR bodies and 5 lenses, but found myself using the Nikon 200-500 quite a bit, especially for birds. Great lens for animals also although you will often be too close to lions and others. Have a great trip!

I recently returned from my second trip to Africa--The safari was to Zambia, Zimbabwe and Botswana. Previously we had been to Kenya, which was a great viewing area. But Botswana was a home run--absolutely wonderful. We had several people we did not know on each safari and none were photographers. However they all were fine with my desire to take good pictures. I learned very quickly that you should ignore them and take your best shots. Sit in the row behind the guide. Ask him to stop when you see a picture. He will and will be very helpful and patient when he realizes you are serious. Make sure you have a phone or pen and pad so you can notate your shots--what was that bird or animal, ask your guide--as you will have trouble recalling all of this later and often you will go through periods where you just keep seeing exciting shot possibilities. (A cooperative spouse is a great help.)

I too shot Nikon and I have the 800 with the f/2.8: 14-24, 24-70, 70-200, 2x teleconverter, and a couple smaller specialty lenses. For the most recent trip I added the Nikon f/5.6, 200-500 and it performed great. It isn't as good as my three regular lenses, but took great close ups and became my go to lens. B&H recommended it for a safari rather then Nikon's or other makers much more expensive and heavier long lenses. I also took a second camera so I wasn't changing lenses all the time. And no tripod as you really can't use one. A remote trigger is helpful and make sure you have stuff to clean your glass and keep it dry during rain!

Have a great time.