A first safari? I brought a .500 NE double on my 1st safari and yes, I knew very well how to use it!! Go big or go home!!!!
In the interest of full disclosure, I also brought a .375 H&H as a plains game gun and a backup rifle in case my ammo didn't arrive at my destination courtesy of the airlines.

For solely plains game hunts, I’d likely bring a .30 caliber such as a .300WSM or maybe a .375 H&H.. The future will tell what I do.