I am considering an custom takedown bolt action rifle in the future with a Mauser action.

What would be the best combinations to consider with the most usage.

30 cal what and 375 H&H ??

300 Wby and 375 Wby??

300 ultramag and 375 ultramag??

30-378 WBY and 378 WBY??(?gag!)

Any ideas??