About bullet selection,,,What if the angle is not as one wished for a broadside? I question the use of a light weight 325 gr. (light for caliber) with a sectional density of just over .221. That's akin to using a 30 cal, 150 gr.,,I don't see or hear of that being used in many elk camps. I wouldn't go below 400 gr and prefer 420-425's myself. I just don't know that a 325 or a 350 would make it through the front shoulder if need be. That weight cast hard, maybe?
I would opt for the Remington 405 gr. FP load. A good tough bullet, and with a .458 FP, one really don't need much expansion.
As far as range goes, I would set up a 8-9" gong, backing up untill I can longer put 3 consecutive rounds on it,, and routinely. That leaving the prior distance as my max range. That method, leaves some margin for error, or if murphy shows at the wrong moment.
Dave