I did the same last year. The main, big purpose was buffalo, but I also had some PG "want-to's" on the list. I was accepting the fact that I would have to give up some of the reach of other calibres. So if that warthog/steenbok turned up 200 metres out, I'd have to tip my hat at it and say "Another time". The 404 isn't really a long-range, across-the-valley cartridge. And mine was scoped with a 1-5x24.
In the end, most of the time was spent on getting the buffalo, and the only other game hunted with the 404 was an impala. (Not counting dispatching of a sick kudu calf at point blank range, i.e. at a range of 1 foot or so).
To get back to your 'real' question, I know that NF have some pictures of their bullets and how much they have expanded at various impact velocities, but not for all calibres/bullet weights. I'm quite certain, though, that 2000 fps at impact from their 400gn should give you enough expansion for any plains game.
You could go lighter - I believe there is a 340gn option as well (availability uncertain though - I would guess that 400gn bullets account for the majority of the production).
Or do as I did - bring a mixture of SS and PP.
In the end it all depends on the biggest thing you're planning on hunting. You could always bring the 9.3x62 if eland (or similar) is the largest animal you're after.