I've only been out west one time, to Colorado. I took a 30-06. I normally shoot 150 gr.p.s.p. for whitetails. For that trip, I went to premium grade, 165 gr. extended range boat tail bullets. And a lot of trips to the range. Unfortunately, I didn't get a shot at an elk to test effectiveness. The other three guys I went with used 7mm, and 300 mags.
A Western hunt for elk, be prepared to take a long shot. A flat shooting rifle is your best bet and yes, a quarter bore will kill an elk, witnessed it a few times, but a 30 cal rifle would serve you better if you are prepared to practice shooting it at long ranges.
I have taken several critters out west with my 25-06. It is a flat shooter and I took a summer before heading out the first time and shot it at long distances, not less than 200 and out to 500 most every time I shot. I sent hundreds of rounds downrange working up a load and proofing it at long ranges and that load shoots less than a half MOA all day long, but... for an elk, you need a perfect shot with that little bullet and it would not be my first choice for a rifle elk hunt. (I'd take my 308)
I prefer a bow and a distance of less than 60yds...