As silly as it seems, if Africa is on the horizon, I’d go with more than a 30-06. I’ve not gone one-gun for plains game alone, so my minimum one gun has been a 416, but if I WERE going without something big in mind, it would be a 338wm, with a heavyweight bullet 300 as a respectable second place in my mind. Most of us just don’t get enough opportunities to go over, and I would hate to come back with ANY regret on the VERY OFF CHANCE anything didn’t go according to plan with a lesser rifle. A 270win or 25-06 would be fine for almost any plains game, without question, and I’d likely use a 6.5 PRC or even a 6 creed maybe myself if I were walking out my back 40 to do it, but for the time, money, and opportunity, I’m prone to hedge my bets HEAVILY. My shoulder will tolerate heavy recoil a lot better than my heart would tolerate regret of a sub-optimal performance on game during a “hunt of a lifetime.”