If we're talking ultimate elk cartridge up to 400-500 yards it's going to be pretty hard to beat the 378 Weatherby. It has flat enough trajectory for pin point shot placement and a ton of energy when it gets there. I've owned one, I didn't like paying $5 dollars every time I pulled the trigger. That was a major set back and I should of reloaded for it.
The is no substitute for proper shot placement. None, zip, zero. Practice and knowing your rifles trajectories are worth more than any amount of bullet weight flung down range. Elk aren't that tough until you blow a front leg off one and try to run it into the ground to get it killed. You better eat your wheaties for that experience.