I voted for the 450/400 as I think it is the best choice for the modern Safari hunter.
I have used the 9,3x74R, the 450/400 3 1/4", and the 450 No2 in Africa.

All have given excellent performance on a variety of game. I have taken plains game, buff and elephant with all 3.

The 450/400, especially if scoped, is the best all round choice.

If you are shooting mostly plains game, a buffalo, and maybe a cow elephant the 9,3x74R will serve you well.

If you African Safari revolves around multiple elephants, multiple buffalo, then a 450 or up Double is a good choice, IF you can carry the extra weight and take the extra recoil.

Hoewver,
You can NEVER go wrong with a 450/400 double.

It has all the power and penetration you need for ANY game.