If this will be your only time over to Africa, get a good 375. A Winchester 70 Safari Classic is a very good choice.
If you'll be going back after dangerous game several times get the same rifle in 416Rem or a CZ 550 in 416 Rigby. Have two scopes for your heavy gun...a fixed 2 1/2 or similar and a good quality 1.5-6 variable. Sight the 2 1/2 in for 75 yards and the 1.5-6 for 200 yards with lighter, faster bullets like a 300-350gr for the 416 for PH hunting as a second gun to your 30cal.
In the 375, a Ruger Safari is a great and economical choice, also. Do the same as with the 416 with whatever 375 you get, if that is the choice.
Mount the scopes in good quality DR mounts, so you can use open sights for very close in work if necessary and for simply having a spare and one for closer work, with the other for longer shots with lighter bullets.
Sorry for the poor photo. It is a scan of a smaller photograph. I took this buffalo with a CZ 550 416 Rigby and swear by the 416. I've also used a drilling in 9,3X74R and an FN action Sako in 375 Wby. If elephant and hippo are on the menue, the 416 is a better choice.
I don't really like the 458 Win much. It isn't flexible like a 375 or 416.
Thanks again for the great input. Another vote for the 416 Rem Mag from someone who has been there. Very good to know. Thanks for the advice on the set-up. I really appreciate it.