Doesn't just knowing that a particular rifle shoots well give you more confidence in the field, I imagine it would, especially putting 3 shots on a buffalo so close together.
It's like that for me in the comp shoots, if I know that the rifle shoots inch groups, then any odd shots that might appear on the target are all my fault.
A lot of what I do when reloading might be helping, might not either, but if you can get it into your head that by doing "X" to the rifle or ammunition might make it shoot or perform better, you will hit closer to the centre.
All in the head, the brain is a very powerful thing.
(The book Competitive Shooting, by the Russian coach, Yuryev, goes into the physcology of shooting very well, but the reading can get a bit heavy at times)

In any case Empire 375, buy whatever calibre cranks your tractor, either of them will be fun.

Regards,
David.