You don't state your level of physical fitness, or your hunting background, so I will qualify my thoughts and be more long-winded than I might otherwise be.
If carrying a standard weight rifle will be burdensome to you, you may want to go to a lighter rifle, but when shooting magnum rounds a light-weight rifle can be punishing — at least in practice. (You will never feel the recoil when shooting an elk.) I also find a standard-weight rifle easier to shoot well when I'm winded and a light-weight rifle would be bouncing with every heartbeat.
There are people who take elk with .243s, so yes, a smaller round CAN kill an elk under the right circumstances with a perfect shot. Elk are BIG animals, especially a bull that has his muscles pumped up from the rut. I've seen a premium bullet from a 7-mag not penetrate the ribcage on a close-range shoulder shot. I've seen elk not even flinch on being shot. Putting these observations together, I am certain that many "misses" elk hunting were not misses, just kill-shots that will take 3 days to be effective.
An outfitted elk hunt is a BIG deal to me, something I don't get to do often. I don't want to be on the hunt of a lifetime, have a shot that would be "reasonable" with the right rifle, and not have a rifle capable of that shot. For that reason I'll never again hunt elk with less than a .300 mag. I took my last 2 elk with a .338/.378 Weatherby Accumark as both were at a full run through the timber. I knew I didn't have a perfect shot on either, but I knew the magnum would put them down. Both tumbled to the ground instantly when I pulled the trigger. Both times the guide was as impressed as I was with the rifle's performance.
Guides tend to over-estimate shooting range before a western hunt to convince their potential clients to be prepared for the possibility of a longer-range shot. I've been told by the guides that they do this because otherwise they get hunters that have never shot over 100 yards and freeze up on great shots at ranges well within their rifle's capabilities. In reality most elk are shot between 30 and 200 yards — well within the range of a .30-06. (I shot my biggest bull during the peak of the rut at all of 9 yards.)
Most elk guides I've talked with and worked with tell people to bring AT LEAST a .270 Win., and that being comfortable with your rifle is more important than the size of the cartridge. I agree with that, although I would add that the hunter also needs to know HIS effective range with the rifle he is carrying. If you are comfortable with your .30-06 and are comfortable knowing there may be shots you should not take with that rifle, it is an excellent choice. If you want to maximize your chances of bring home an elk, you may want a more powerful cartridge.
Whatever cartridge you settle on, be sure to use a bullet that will penetrate to the vitals from any angle you may be shooting from! With elk, PENETRATION, is the most important measure of a bullet's effectiveness.
You don't mention your optics. A quality scope on your rifle and high-quality binoculars should be a given for a guided elk hunt. I bought a new pair of Leupold binoculars before my first elk hunt — and returned them to the store as soon as I got back. They were not good enough for me to judge animals at a distance. I now own Swarovski binoculars.
One thing guides don't tell hunters — in most areas only a third of hunters will get a shot at a bull elk. The most important thing you can do to increase your odds is to RUN now. Cardiovascular stamina often separates hunters who don't have a chance from those that do.
I hope you have a great hunt and come back with memories for a lifetime!
