I've easily killed 100 animals in Africa with a 7x57 shooting 175gr partitions. They drop like mortars, and its still just fine. A 300WM has a MPBR that is astounding by comparison. The idea of a WSM or some other rifle is totally unnecessary and I've not seen a WSM or WSSM rifle that was stocked and scoped correctly for Africa-style hunting anyway.
I'll tell you what WILL screw up your hunt though, and its not caliber. Its stupid long-range gun stocks with their monte-carlo combs, with extra high rings, and big glass on top. Sure they work at home shooting prone, or at the range from a bench, but while you move your face around trying to get comfortable on sticks, then mess with your head angle to see through the telescope, then mess with the dial lowering it from 12x to 2x power, the animal standing at 40 yards is LONG gone. I'd wager <1% of the new rifles at Cabelas are suitable for Africa hunting by virtue of their stocks, optics selections, and ring selections in their store.
150gr-200gr bullet hitting an animal at least 1900fps with a scope set at between 1x-6x power is all you need for 99% of the shots in Africa. Lets not take the exceptional 1% case and make it the normative case. Pick your rifle with the lowest rings and fastest target acquisition optic in the lowest comb stock possible. The caliber that happens to be is not particularly high on the priority list and is less important than bullet selection.
14 trips over there, total amount of shots taken prone: 1. (and it was an eland in a velle and I was on a goma, about 200 yards diagonally way down) Farthest shots taken: Bushbuck at 345 yards with a 375HH off sticks, then a hyena at 265 yards, then a couple impala at 220 yards, the prone eland shot at 200 yards, and everything else was 150 yards or less. That's 14 trips, over 220 days in the bush, and the sample size just doesn't support the need for a sharpshooting rifle, you need a stalking rifle.
Speed of getting on the animal kills animals, not long range shooting technology. How fast can you be ready? It better be really damned fast.