RWS loads for both the 9.3x64 & 375H&H are in the very warm to hot region; true there is virtually a cat's whisker between them at the muzzle (293gn at 2575fps & 300gn TUGS at 2590fps respectively), its only out to about the 150m mark that the 9.3 starts to get in front & then pull away - these are the same projectiles buy the way.
This makes both of them very good especially for plains game with these proper sporting projectiles.
Yes their case sizes are completely different & hence being a larger case the .375 will have to be loaded to a higher capacity to get to the same equivalent pressure, or run at a lower pressure with the same load as its German twin resulting in less performance.
Basically the 9.3x64 is the more efficient round for the performance level that it obtains & doesn't need an action modified to be fitted into.

Good as they are, & they are good cartridges in their own right; the 9.3x62mm still shades the .35Whelan behind - but both are definitely a step behind the 9.3x64 & 375H&H.
Yes there are some who load to insane levels to claim, mine is better than yours - sorry but I have got to factory specs & that is just fine by me!

As a note this info is taken out of the 2007 catalogue when they even advertised .404Jeffery Ammo.
So yes Rule303, I do so heartedly agree!
Cheers
93x64mm