I have only a few ideas to mention. #1 the 35 Whelan in a handi. .....FTF possibly. On dangerous game, or even just expensive hunt. #2, I have heard that 375 is a minimum caliber in many countries in Africa...... 35 would be illegal. The 500 would pass.
True, in a bolt, the Whelan is a much better long range gun, no question, but up close, within 100 yards, I would take the 500.
I cannot swallow the 1 gun scenario, especially since you can have an extra barrel here for about $130 average. In this case I would get a 35, use the 225 gr loads, put a scope on it, and get a ghost ring peep and large fiber optic front sight on the 500. And for the price of a decent bolt you could probably also pick up a 280 barrel which @ 26" will crank out 160 gr range bullets at a top velocity.