Hydehunter - I would highly recommend you contact the PH where you will be hunting to confirm a caliber smaller than 7mm is legal in the Province you'll be hunting in. While RSA does have a national hunting "ordnance" that specifies minimum caliber or minimum muzzle energy for particular species, each of the 9 provinces are able to have their own "ordinances" and "proclamations".
https://phasa.co.za/2018/05/15/provincial-ordinances/Also, keep in mind that some regulations may or may not apply to "local landowners" or local RSA biltong hunting but DO apply to foreign hunters.
