My wife and I are going on safari to Tanzania later this summer, and I'm hoping to capture some good pictures of the wildlife (as well as usual tourist and landscape shots). I've never been on Safari before, so I'm looking for advice about what lenses and gear in general I should bring.

I use a 5DMkIII, and the longest lens I currently own is a 70-200mm f/2.8 IS. I've heard that for serious wildlife photography I really should be looking at 300mm, 400mm, and up. There are a few different options, and within reason I'd be happy to buy (or rent, for more expensive gear) whatever the right tool for the job is. However, a big restriction I have is in the total weight of gear I can bring - plus I'd be super nervous about bringing more than I could hand-carry (the thought of checking expensive lenses on internal African flights that are notorious for losing bags makes me shudder).

Given the restrictions, I can basically only bring two lenses, maybe three if one of them is really small (I could probably slip a 50mm f/1.4 into a pocket somewhere, say). My intention is to bring my regular walkabout lens, a 24-105 f/4, in addition to the 70-200mm as my long lens, and then also bring a 2X extender to get extra reach on the 70-200.

Does that plan make sense? Would I be disappointed with the image quality from using an extender? Could I get away with a 1.4X extender, even? Do I need to achieve a longer effective focal length than 400mm to really be happy?

Assume I'm more interested in larger beasts than in birds, and that my quality bar is "discerning amateur" (i.e. not looking to compete with a wildlife pro, but want pictures I'd be happy to print at a decent size and hang on my wall).

If you do recommend a longer lens than the 70-200, which other lens would you pitch off the boat to make room? Assume I need at least some capability to take pictures of stuff other than lions (we have a few days on the beach, etc.).