Hi Norfolk,
Personally I would stick to the bolt action .375 and put in for a bigger caliber in the double for the more up close dangerous game. I understand that you can't have expanding ammo in this county but you can either get it sent to camp or if you are a hand loader like you say just buy and bring a box of heads back with you when you are in Africa next, you can load as much as you want and it will be a quarter of the price trust me
As for the heym or the krieghoff, both are great rifles but I would go for which ever one is an ejector personally as you could possibly regret that in the heat of the moment when something is running in full charge at you and your fumbling around trying to extract empty brass!!! I have a couple of PH friends that have krieghoffs in .500 nitro's and they swear by them, so they can't be bad!!
Food for thought