I killed my bull a couple years ago with a cheap 180gr Remington Corelokt out of my .300 Win Mag. Also several antelope and mule deer, same load. You don't need a premium bullet to drop an elk, shot placement matters a lot more.
Kudos to him for establishing what his effective distance is! I hate to hear all the stories from the outfitters about morons who are willing to take wildly unrealistic shots.