Hemi:speed has nothing to do with killing and often a faster bullet will penetrate less. Some guys on here can even explain this. You are going heavy with a reasonable wound channel with a .325 which is a responsible choice considering the guns .458 guides. You want a big slow bullet for maximum penetration and the 250 grain will get er done!
With good bullet construction speed is a wonderful thing and has a fair bit to do with killing in my experience. The great thing about the 325 is that you can get a pretty good balance of both with a 200 grain bullet at 2800+ ft/sec. That speed will give you excellent expansion and a wide wound channel and the retained weight of a Nosler Partition, Accubond or Barnes X will give excellent penetration.
