I still think the term "all-round" is important. And a 300 to 350gr .408 to .423 projectile is not an "all-round" medium game bullet.

The 400 or 410 gr projectiles are excellent for dangerous game especially buffalo though.

The .375 with its 200 to 235 gr bullets, or up to 270 gr bullets makes a reasonable choice for medium and plains game. Over powered in some cases, but still acceptable.

The 300 to 350 gr projectiles make good large and dangerous game choices.

Assuming loads could be made which regulate well enough. Otherwise for the lighter bullets, a single shot from one barrel approach could be used.

Recoil is also a factor. Every step up and the recoil increases and for some, accurate shooting decreaes.

For me a .375 Flanged double rifle with a proper choice of scope would make my dream desired all-around rifle for hunting most beasties throughout the world.

A .400 double rifle would be the next choice and a fine almost all-round rifle, a little more on the heavy side.

Just my thoughts on it.