since you've picked those two, the obvious choice would be the .416Rem. .404 bullets (.425" or .423"?)) will be more difficult to find along with brass and dies being much more expensive etc.
; Too, RCBS makes a descent mould fo rth e.416 for heavy bullet cheap practise. Hrdened wheelweights and a good lube will take full power loads in the 2,500fps range. I suggest Lyman's Moly lube.
; In .416, My choice would be the .416Taylor. Simply neck up .338 or .7mm mag. brass or neck down .458's - easy as can be. About duplicates factory .416Rem however works in a standard Mauser length action and uses about 10%(or more) less powder to do the same thing.