Con,
Have seriously considered the 10.75x68 but elected to stick with the 404 as I have accumulated some 404 items for some time now. Such as a Recknagel 404 Magazine and components pus a Walther Barrel. Although the 404 is in the similar power range, it will be fitted with a scope where the 425 and 458 will not. Thus making it a little different than the other two.
Besides, this rifle will be used in areas that aggressive Elephant will be encountered and IMO a 404J with 450grn FMJ bullets with a MV of around 2200fps would be a safer bet than what a light 10.75mm with 400grn bullets traveling at around 2150fps would be.