The .405 would be my choice. The larger the bullet diameter, the better 'effect' rifles have on tough game. Rifling twist for a 350gr. bullet would be about perfect - about 18" I think would work just fine. Faster than this isn't necessary.

If the rifle was to be used for a lot of ungulate shooting, more so than bears and buffalo, then a 9.3x74 would also do the job and be better suited for shooting to 300 yards.