Hi Tom! So exciting to read about your incoming trip!
As for focal lenghts: I've never been to the Okavango, so I'm not quite sure about the FL to use there... there are surely some ppl here with experience on that area that can better point what's the choice for the Delta.
But for the Chobe River itself, I'd take the Z800 and a zoom covering somewhere up to 400mm. I don't need to have all mms covered, a gap of 400mm seems a lot but it isn't if the glass is good enough and you're working with 47mpx...
Last March, the combo I took was the Z800 and the 180-400 f/4 TC. It's proven to be the best combination for me, yet 800mm was too much sometimes, so I had to grab the 184, however, having the prime forced me to become a bit more "creative" to take the shots...and it wasn't too bad.
For this last trip I took the Z600TC only, and I've been happy with the choice of having 600/800mm (840 to be accurate), however, I missed the 184... (I damn myself since we had a leopard sigthning that chose the closest tree... and the 600 was excessive...)
For wide angles I took a Z50 with a DX Z18-140mm and... auch. Not doing that again, I'd much rather have a 24-120 f/4 instead. The performance (to me) was very compromised by this combo.
Haven't tried the 24-200 but on paper, that'd be a good choice I guess. However, perhaps a 70-200 could do better, yet, I believe that a 24-120 is just perfect to use for everything close enough that would not fit with 180mm'ish. Ellies can get very very close to the boat...
As for weight: depending on the long haul airline and the ticket, you might be able to bring 2 x 12kg backpacks in the cabin.
I didn't have any problems with the weight of the in-cabin luggage with Airlink (or SafariLink).
You stand your ground telling them that there are valuable equipment (glass) and they'll go for it. For bushflights, it's not a big deal to hand it over to the cargo compartment, you'll see more often than not the bag being loaded and unloaded from those small plains on site, sometimes you load it yourself!
I fear totally the big airlines and airports though. I wouldn't check in anything valuable on the travelling suitcase (only replaceable stuff).
Hope it helps with your choices!
Krgds, Marcelo
ps: Here's an example of what the Z50 could do combined with the 18-140... shot at 68mm (102mm on Fx)
DSC_1129©MC by
Marcelo Cinicola, on Flickr