In my humble opinion you should seriously consider engaging another PH. Shooting a handgun (Biggest Finest Revolver) at a Cape buffalo is the heighth of folly. Only slightly less misguided is shooting with an unfamiliar rifle. Whatever rifle you use, the most important factor is being able to hit with it where you want to hit, under the most unexpected and trying of circumstances.

Find the rifle you want and practice, practice, practice. Find an unoccupied area of land, a gravel pit, a clay pit, an abandoned quarry and shoot, shoot, shoot, until you can bring the rifle up from the carry position, release the safety, line up the sights with each other and the target and release the trigger all one sooth motion.

You don't need to expend ammunition at first to do this. You can fix your gaze on a doorknob, on a light switch on any other discrete target at home and practice the same skills with an (verified) empty rifle before you fire the first shot out of doors. The goal is for the sights to align themselves on the target without any conscious effort on your part, just the way you line up on a quail from a flushed covey.

Remember, the PH is not always there and if he is, he may have other things on his mind than protecting you, such as protecting himself.