Once in a lifetime elk hunt? May as well use your deer rifle with heavy for caliber quality bullets. Example: 30-06 with 180gr Nosler Partitions.

There are some " ultimate" elk rifle/cartridge combinations out there all right but for most folks, all too often:
1. The rifle costs too much
2. The ammo costs too much
3. They weigh too much
4. They kick too much
5. The muzzle blast is too much
6. They get folks upset too much

As you can see " ultimate" is just too much for most folks. If you are not allergic to the word Magnum and decide to break free of the crowd, then ultimate will have to be crafted by you not for you. I' d recommend " bigger, faster, stronger" .

Bigger than a 30-06.
Faster than a 30-06.
Strong bullets.

Beyond that, the rifle/cartridge combo will have to be yours according to what you can handle.

A place to start for a general statistical cross section of the folks on this forum might be the " Whats Your Favorite Big Game Rifle?" poll in this section.

Never Go Undergunned
EKM