Thanks Russ for your reply. I previously missed your response. Interesting comments.

A .375 H&H Flanged is of interest as it is a "mainstream", well sort of, cartridge. Perhaps too similar to my 9.3x74R? The idea is a one world rifle for everything from medium to big game. A plains game rifle to a in the thick stuff rifle. Not too powerful for medium game hunting, but still acceptable for buffalo and maybe elephant.

Should it be a .375 H&H Mag rifle for ease of ammunition supply if needed? The extractors might be an issue? The Valmets take rimless cartridges already in barrel sets. No magnum belts though.

Instead of 375, or a .450/400, maybe a .416 Rigby No.2 Rimmed ?