If you read hunting and shooting magazines and the authors recommendations for Elk then you will be looking for magnum caliber of some type.
The truth be known if you have a Whitetail rifle you shoot well then bring it.
The key to putting Elk on the ground is Shot Placement and bullet performance.
A lot of Elk are missed or worse yet wounded and lost because the guy behind the counter tells you this big super stomp whacked magnum is just the right tool for elk.
Yes Elk are tough but think about a few things here, back after 1895 the year the .30-30 came out it shot a 160gr. bullet at a blistering 1900 fps, Guy's would kill Elk, Shoot Griz Bears with it cause no gun writer was saying it is to small.
Where I live in Wyoming during the Depression most could not afford a rifle so there was a community rifle, this rifle was a .25-35 WCF, it was used to kill everything from Pronghorn to Moose. Today people are using may be a .243 or .30-30, both kill Elk and Moose with a well placed shot and a good bullet I do not hear of any lost game using these two rifles, Shot Placment is KING!
So do not be afraid of bringing your whitetail rifle to kill an Elk.
If you do then you may very well be able to shoot it well, and that is 85% of the battle.
No way for me. Everything would have to be perfect to make an ethical kill with that size caliber. In reality, most opportunities are less than a perfect position, distance and shot placement. I would stick with the larger and heavier calibers to make up those margins of error.
Just my $.02