There's a lot of game in Africa that are really not large at all. You already have a .375 and that will handle the larger plains game well.

For animals under the size of Gemsbok and I'm talking the Impala size and there's a lot of species that are that size one could consider the 7MM Mauser, 280 Rem, .270 Win or even the 6.5 X 55 or 6.5 X 57 as the light rifle.

Personally if it were me I'd use the 500 Searcy for the "stomp your ass" game and get a 338 mag as the second rifle and the 6.5 X 55 for the light rifle.