Ian has the bullets right
You need a bullet that will hold together. So I think Ian's choices are better than the Nosler partition. The Partition might kill better on a broadside shot into the vitals. For that matter, the 300 SMK would likely kill great on quartering away shot where you could stick it into the vitals from behind the shoulder. But it's not the right bullet for your hunt!!
If he's pointed in my direction, I'd want something designed to retain nearly all it's weight. That would give the bullet a better chance of penetrating large bone and muscle before it reaches the vitals. And the best shot will break a large bone AND reach the vitals. So you need a bullet capable of doing just that.
I too would take a 416 RM if I had one. But I think a 338 RUM is plenty of gun if the first shot is right. Beyond everything else the first shot has to be into the vitals and, if possible, take out a front shoulder. That would be all I'd be thinking about when it came time to take the shot. If I wasn't 100% sure of that first shot, I won't shoot until I was sure. I'd never shoot the first shot unless my hold was dead steady and I was sure where the vital area was. I'd also never open hostilities on a moving animal...unless he was very close and headed straight at me. Then nothing, not even that 416, would seem big enough!! But the 338 and the right bullet will do the job if you do yours, even on a close in charge.
If I just build a 338 RUM, I won't take anything else. Have a good hunt!!