Were it my rifle I would stay traditional Brit and go with a .375 Flanged Magnum. Basically the same as a 9.3x74

Now if you don’t want to hand load the 9.3x74 seems a better choice just because availability of the .375 could be very hit or miss.
Of course it also depends upon whether the maker will do one in .375 Fl Mag?

Just my 2¢ (or 2p)
- Mike