It will definately do the job with a good bullet and a good shot, but like others have said, there is a lot better calibers for elk then any quarterbore, 257 WM or not...
Also with elk, you rarely get that perfect broadside shot, and you get maybe 1-2 chances at elk in a season so you better be able to make the most of them. Its just a safer bet on your part to be able to bring the biggest rifle you feel comfortable shooting and be able to make smart choices on the shots you do take if you choose to bring a smaller caliber.
I personally have shot all my elk with magnums such as the 7 RM, 300 Win Mag, 300 RUM, 338 EDGE and go for the shoulder or high shoulder shot to anchor them where they stand so they dont run halfway around the mountain and end up in a worse spot then they already are. Elk are big tough animals and can go a lot further then most think on adrenaline with no lungs...
My personal lower limit on elk is a 7 RM with a good 160g bullet. I shot a few with the 300 win and RUM and like them, but the way my 338 EDGE lays them down makes me a firm believer in 338s for elk.
Now I know you dont need a magnum to kill elk, you just have to limit your range a bit. Where I hunt elk, your typical shot is going to be no closer then 300 yards out to as long as you care to shoot, so I"m set up with magnums shooting heavies. But that depends on your terrain and your own personal limits and what not. If I knew I wasn't gonna be shooting any further then 500 yards, Id be ok with a 270 or 30-06, but I have the option and ability to shoot from 1K-1200 and those cartridges just wont do it for me.
Theres a difference between real elk hunters and your so called elk hunters...real elk hunters are the ones that are out there every year filling there tag every year or every other year. THink I read an article in a magazine where it was the same 10% of elk hunters are the ones who continually harvest 90% of the elk, theres good reason for that.
Like you say, gives you good excuse to go buy another rifle, cant beat that! Stick a good 160-175g bullet in that 7 RM and you'll be fine on any bull in any situation out to as far as you probly care to shoot. You cant say the same with the 257 WM.