If the PH in your story:
1) Is the first in his family to hunt, he'll shoot a worn out BRNO 458 that he got second-hand from the game department;
2) Is of a line of PHs, he'll shoot a Rigby 416 for a bolt, or an Evans 470 for a double - these only when acting as a PH - otherwise he will shoot everything with a Rigby 350 or 9,3x62 - depending if he is from British or German lineage.
3) Is a man of taste and simplicity, a Rigby 416;
4) Does more elephant hunting than anything and finds himself all-too-often cleaning up his client's mess, a 458 Win Mag - one he had made by a lower-cost (read non-British) firm, but is otherwise 100% reliable;
5) Is over 6' and 220 lbs., he'll shoot a 577 Nitro;
6) Is a double rifle devotee and has a soft spot for the black powder guns his father used, a Rigby 450 Nitro (because it spanned black to smokeless powder);
7) Is an American who lived his dream of becoming a PH - a 375 H&H or 458 Win - either in a Model 70 - with a nod to the 375.
That should help ;-)