I've only a 9.3x74R and have only used the 286 gr weight, Woodleigh Weldcore PP and FMJ. My velocity is only around 2170 fps, very mild. But 14 water buffalo, and some scrub bulls have fallen to it.

I think a 320 gr or heavier is too much for this cartridge, or at least my loading of it. As mine is also a DR it's a pain to adjust the barrels for regulation if needed.

9.3x62? I don't have one so can't say, if it's too heavy.

If I had a 9.3x64 I would seriously consider the 320 gr weight.

One day I'd like to try the 350 gr in my .375 if it develops enough velocity.

Heavier bullets are an interesting proposition. Increased SD means potentially increased penetration. Notwithstanding that increased calibre size, i.e, bullet width, is also a killing factor, a 320 gr 9.3 should have increased penetration. Same as a .375 350 gr. A .400/416/404 450 gr. A .404 or .416 450 gr is so close to the .450/458 480 or 500 gr.