I lived in Colorado for 7 years and soon found out what works and what doesn't for mule deer and elk (moose too, but I never hunted them). In theory, a 270 is nothing more than a 30-'06 necked down to 27 cal. In practical use, the 270 takes advantage of features found only in a handful of cartridges. The heavier 270 bullets have high sectional density and high ballistic coefficient. This combination makes for excellent penetration, expansion, and accuracy.
If I had to choose just one gun for all big game hunting needs, it would be a 270 Win. Side-by-side comparisons to other cartridges may favor the other cartridge in a few categories but if you look at the overall picture, the 270 comes out on top. The other non-magnum cartridges with near equal performance are the 6.5X55 Swede, 7X57 Mauser, and the 280 Rem. Yes, you can go to the heavy magnums and get more performance with brute strength but in a standard rifle with a standard cartridge, a 270 is hard to beat.
I don't agree with your scope selection but then it's not my gun. If you hunt a lot, you'll find the higher power scopes have too many disadvantages for the single advantage of magnification. Personally, I hate scopes with an AO for hunting. You never know what distance your shot will be so you find yourself trying to make adjustments while Bambi casually trots off and you miss your opportunity.
Here's some things to consider for a hunting scope:
Eye relief: The range of distance your eye must be from the lens to get a full view. The more powerful the magnification, the more narrow the eye relief gets. This makes it very difficult to shoulder the gun and find a view in the scope. At 4X you'll have at least 1.5" of eye relief range. This means your eye can be anywhere from 3.5 to 5" from the lens and still get a full view. At 12X, that narrows the range to about a 1/4" sweet spot. Your going to spend valuable time just trying to get your eye to find a view.
Field of view: As magnification increases, your field of view decreases. Field of view is rated by how wide an area can be seen at 100 yards. With a powerful scope, you will have a hard time locating your target because you can't see a large enough area. At closer ranges, all you see is hair and you won't know if you are aiming at the head or ass.
Light transmission: The more powerful the magnification, the less light is transmitted through the scope. To compensate for this, manufacturers use a large objective lens. Though it fixes one problem, it generates several more. The scope will be longer, heavier, and will require higher rings to clear the barrel. Higher rings move the scope farther above bore line so the trajectory doesn't track as well. Additionally, higher rings make the scope more sensitive to recoil and position the scope above normal eye level.
Parallax: With scopes 9X or less, the factory presets the parallax to 100 yards. With scopes 10X and more, parallax won't track so an AO ring is required. Parallax amounts to having the cross hairs in the proper focal plane. The more parallax is off, the more cross hair drift you get. The higher the magnification, the more parallax is affected. Clamp your gun in a vise and position the cross hairs on a target. As you move your eye up/down, left/right, you can actually see the cross hairs move on the target when the gun is totally stationary. When parallax is adjusted properly, you won't see any cross hair drift. If you get cross hair drift because your eye wasn't positioned exactly centered, your groups will drift and give the false indication of poor accuracy. When hunting, you usually don't have time to play with the AO ring to correct parallax.
Wiggle factor: The higher the magnification, the more wiggle you see and the harder it is to hold on target. For me, 4X is about the most I can handle without a rest.
Despite what you may read, a 270 has a max quick kill range of 200-225 yards. Any shot beyond that is iffy at best. No doubt, deer and elk have been killed at considerably longer distances with a 270 but more times than not, you will wound the animal and it will run off and die. Using the standard of 1X per 25 yards, and a range of 225 yards, a 3-9X scope is just about perfect. I always keep my scope on the lowest X setting. If game is spotted at a long distance, you will have plenty of time to adjust the zoom ring. If something jumps up close, you don't have time to find the target in the scope, adjust the AO ring, play with the zoom ring, and take the safety off. You need to be ready for action immediately.