I did overlanding (in SA and Namibia) with a Pajero 3.2D-ID SWB in Automatic.
What a brilliant experience with no changing up and down on gravel roads before and after bends (of which there are quite a lot), no sand and deeper sand patches, as well as short up and downhills etc .
It depends entirely on you whether you prefer tranquility while driving or constant gear shifting and de-clutching. Even in deep sand , automatic in the 4×4 context is preferrable, provided you can override the auto box.
In summary , normal overlanding with a manual or automatic box 4×4 is a personal choice, however if you maybe progress later to serious rock obstacle driving or the van Zyl’s pass experience a manual might be preferrable.