There's nothing wrong with your 30-06SPRG. A 180gr bullet in the 30-06 has more energy at 500 yards than a typical 170gr bullet in 30-30 at 100 yards and the latter is the standard by which all other calibers for North American hunting are measured for distances up to 150yards.(and at that range, the 30-06 still has more energy at ~650yards) If the shooter is up to the task, then some hardware upgrade will be in order particularly in the reloading department to achieve the accuracy necessary. For perspective I shot a match using a 2.5-10X Leopold Mk4 shooting ~5.5" discs at 600m. When you encounter a game animal under 100 yards, (especially moving) higher magnification will be a curse.
Adding Africa to the equation though you get caliber restrictions often historically being ~375 H&H for some countries: These could have changed the past few years though with the popularity of calibers like 9.3X62 and 338 LM.
Either way, don't let anyone stop you from buying another rifle... there is one for every occasion

and it's more enjoyable when you don't have to compromise.