i have hunted and lived in wyoming, colorado, montana and alaska. i was an elk and deer guide out of Hell's canyon in idaho.
the minimum elk rifle is one that you can shoot well and know your shot placement. i have seen women who shot their elk everyyear with a 243. usiing a super penetrator like combitech's or barnes, it will penetrate even on a quartering shot. as a guide we preferred to see someone show up with a 280 or 270 than a 300 WM or bigger. most people cannot handle the recoil of the bigger guns and get flinchy. plus, a lot of people who have hunted a lot get "bull" fever when they are close to an elk, so we want someone who is smart enough to know their limits and have chosen a smaller caliber/cartridge than one who is trying to show off with a cannon that they cannot control EVERY time in the most demanding situations.
there are elk in the black hills of wyoming and s.d. a first year hunter(teenager) shot a monarch in 1985. several taken there that year, but the majority are in the wind river, teton, and big horn mountains. a reputable guide outfit will willingly and ofter insist on giving out references. get other references from those and talk to people that havent been referenced from the outfitter.
this is an excellent article for the beginner elk hunter. if you were on a once in a lifetime hunt, he has excellent advice. younger hunters wanting to learn on their own or more experienced hunters that feel that they can do this themselves may want to venture out on their own. if you havent hunted in the mountains of wyoming, newmex, ariz, montana, etc. i would get a guide irregardless of how much you have hunted back east. we used to run into these guys all the time in hell's canyon. always got their deer back east and was a legend in their state. more often than not, they went home empty and usually were the only ones who didnt get anything. this isnt kansas, nor the appalacians. weather is severe and changes rapidly. bears and pumas are plentiful, as well as wolves and the like. and elk like territory that would make a dall sheep look twice at and a mountaineer look at his gear. elk are very hard to hunt (barring the occasional camp or road elk) but when you know how they think, they are very easy to figure out. outside of rut, in heavily hunted areas, they will find the most inaccessible areas that no one in their right minds would go into. in some states like oregon, that is often right next to the interstate as they have learned that the safest place to be is often there or in town during hunting season. a guide will know these things that are peculiar to their areas, which areas are not safe to be in, where the animals are moving this year, etc. and they will WANT you to be successful.
hope this helps. have a great hunt.