There has always been debate about the true effectiveness of the Mauser 10.75x68 cartridge, remembering that in the heyday of African hunting reloading was not practiced therefore it all came down to factory ammo performance. The shorter 347gr bullet loaded in the 10.75x68 did not have the sectional density that makes for good penetrating bullets and the earlier bullet jackets tended to be thinner than is used today. Even solid bullets in some cartridges fishtailed and distorted enough to preclude reliable penetration to the kill areas.
The respected cartridges that performed well on big game tended to have long and heavy for calibre bullets i.e. good sectional density.

Maybe of some interest is the image below showing both the 404 Jeffery (10.75x73) and 10.75x68 cartridges alongside the respective 400gr and 347gr bullets these cartridges are normally loaded with.
As can be seen, if loaded to normal OAL, a 'Kynoch' profile 400gr bullet would be seated approximately 4mm deep into the 10.75x68 cartridge powder capacity area, I calculate about an 8.5% capacity loss. Crimping maybe an issue too as the ogive of the 400gr bullet is down in, or close to being in, the case neck. This maybe overcome if magazine length and throating permitted seating the heavier bullets out to a longer OAL.
If a safe load was found for a 400gr bullet in the smaller Mauser case without going overboard on pressure and showing any hint of issues holding the bullet in the case neck then at 2100fps the 10.75x68 should be as effective as the 404 Jeffery was in it's original loading. Of course due to the earlier low intensity loading the 404 gained a reputation as an easy shooting cartridge which no doubt contributed to it's good performance on big and dangerous game. Whether a 10.75x68 loaded to original 404J specs can do the same, who knows.