I think the general consensus here is that the 30-06 is more than adequate. i shoot both and there is not a great deal of difference on impact with similar weights, as stevedscross says, the paper ballistics dont count for as much as field experience and if you are using 150gr/180gr under 300yds, go with the 30-06. I prefer a heavier bullet (personal preference) and prefer the 300wm for that reason, i am by no means a big guy, but the recoil of the 300wm off sticks or off hand doesnt bother me in the least, whereas my buddies 30-06 is a pig to shoot because of the lack of fit!
Off the bench however, there is a noticable difference with the 30-06 and 150gr opposed to the 300wm and 220gr!!
i go with the 220gr PMP rounds with the 300wm and it is very good in my opinion, remember we dont get much choice here in Zambia so I havent shot as many different types as most people here, but i dont think i would be inclined to change too quickly.
All in all, you cannot go wrong with either, best thing would be to shoot both and see for yourself.
On another note, in Africa, there is not much that cant be taken under 300m. If you cant get within 300m, your stalking needs practice.
Over 300m, you are looking for trouble with wounded animals etc (i am generalising here, there are many people who train at long range and have good confidence at 5-600m, i am not one of them).
I also feel that shooting animals at that range in Africa is just that - shooting, not hunting.