The Alaska Fish and Game Department conducted a pretty thorough test of numerous rifles back in the 1980's and published a guide with their recommendations. I used to be able to locate a copy of it online, but can't seem to find it any longer.
They found that the magnums, 375 and up provided the best performance. The 2nd place rifle cartridges were a tie between 30-06 and 300 WM when loaded with 200-220 gr bullets. Lighter 180 gr bullets didn't do nearly as well.
While cartridges like 338 WM and 35 Whelen were OK, they didn't give as much penetration as 30-06. Rounds like 45-70 and 12 ga slugs were pretty far down on their list.
They concluded that if someone could handle the recoil 375 was the best option. But when you factored in recoil and availability they considered a 30-06 loaded with heavier bullets to be the best all around option.
This isn't the same article, but they still recommend 30-06 as the best all around choice.
http://www.adfg.alaska.gov/index.cfm...nting.firearms
Finn Aagard, an African PH and gunwriter conducted an almost identical test on suitable cartridges for larger African game and reached the same conclusions.