I don't have a 338-378 Wby so take this with a grain of salt. I have used all the other powders in you inventory in big magnums so have a real world feel for them.
If it were me, I'd start with Retumbo. Best velocity vs. load density.
If I couldn't get that to work, H1000, then H4831
If you have a bunch of H4831 and you are not using it for some other load it would be a reasonable choice.
Take Aim at Rifle Reloading Data | Hodgdon Reloading
lists loads for all your powder choices.