"What i want to know from you folks are what would you choose and why.
I will be stacking my coins till the time comes for an elk hunt and more to add to the list just one thing at a time."
There are literally dozens of cartridges that will work just fine for an elk hunt. We're living in a time when the variety of cartridges available is truly incredible - and I'm not sure it's for the best. Perhaps too many to choose from? Look beyond the mere ballistics, many different cartridges produce adequate "power" to kill an elk cleanly.
Look at some different factors:
How much experience do you have and will you have with that particular rifle?
Will you potentially use that rifle as a deer and maybe a bear rifle?
What's your recoil tolerance?
Will you handload or rely on factory produced ammo?
What's your preference in action type? Bolt, single shot, lever, semi-auto?
Are you going to spring for a good scope?
In my humble opinion the absolute most important factor in bringing down a game animal is shot placement.
Where they're hit is vastly more important than what they're hit with.
That said, the next most important factor is using a bullet adequate to the job - one that will penetrate to the vitals, and do its job.
Most elk hunting by guys who live in elk country seems to be done by guys with their same deer rifles - although they may tend to use a pretty potent deer rifle. I took my big bull elk with a 7mm Rem mag and a 175 gr Nosler Partition. The rifle was accurate, the 3-9x Leupold was adequate, the bullet performed very well. It wasn't a big, heavy rifle either, just a standard weight sporter rifle, a low-budget Rem 700 ADL with the synthetic stock. Nailed it from about 180 yards, from sitting, unsupported except for the sling wrapped around my arm. The bullet hit right where intended and penetrated completely through, exiting with about a quarter-sized hole. The bull took a few faltering steps, then collapsed. This was very good performance.
The thing is, I could have killed that elk just fine with a .308 Win, a .30-06, a .300 mag, a .280 Rem, even a .270 Win - or any of a number of other decent cartridges. The important thing was putting a good bullet where it belongs - just like in any hunting. Mostly I hunt mule deer, and the sheer size of the bull elk was pretty imposing to me. Big bulls go 700 - 800 pounds easily, as opposed to a mule deer that may be about 200 - 250 pounds, though some are larger. Still, despite their size and strength, a bull elk isn't bulletproof! Sometimes, like other game animals, they have a reputation of being able to soak up tremendous damage and keep going, but still, I'll stand by shot placement being paramount.
The most important factors then in my preparation for the elk hunt were likely:
1. Physical condition - the hunt was from 9,000' - 11,000' ASL in Wyoming. Very tough terrain at very high altitude for this guy. Lots of hiking and riding. Horses helped a LOT on that hunt. Being in shape, so I could get out and scout and hunt hard was very important.
2. Marksmanship - I shoot rifles a lot - many rounds downrange over the course of a year and very few of them from a bench. No benches out there in elk & mulie country. Just rocks, cliffs, logs etc. Being able to handle the rifle well has been a key to what success I've had in the field. On the week long elk hunt, I fired one shot.
3. Hunting where there is game. This sounds silly, but there are vasts chunks of land "out west" where there is little game. Do your homework! BTW, a do-it-yourself hunt for elk is quite possible! The western states seem to have very good Fish & Wildlife web sites, chock full of good info for the hunter.
Back to cartridges - you mentioned the .308 Win. It's a favorite of mine alright - I've shot out a few .308 Win barrels and that takes a lot of rounds. Very good cartridge, many will say it's too light for elk. It will do just fine if you don't confuse it with a magnum. Take a look at trajectory charts, wind drift, power remaining at various yardages and limit yourself accordingly in the field. One thing I really like about the .308 is that it's a mild-mannered beast, which encourages doing a lot of practice since it's not beating you up.
I'll concur with "ryutzy" that the 7mm mag is also pretty easy to shoot. I notice that I shoot a 7 mag easier than I do the typical .300 mag.
Back to the scope - a good scope is very important - you may get one chance early in the morning or late in the evening when light is low. In the years since that elk hunt I've turned to a fixed 6x Leupold with a 42mm objective lens. It's great in low light, and the fixed power scope has worked very well for me on mule deer from 30 - 400 yards.
There, a little wordy. My apologies. But you asked about ELK - and my mind is on ELK right now! As an aside, if I go this year, I'll likely be carrying a .375 H&H, which is completely unnecessary, but I've fallen hard for the big Ruger Number One and want to hunt more with it this year, so I'm going big this year!
Regards, Guy
more like mid west but east of the mississippi. 
