Ooops, sorry, I guess I didn't see that you are not a handloader. Since you are one of the only people on here who buys factory, I'll tell you something that I discovered. I have shot a lot of ammo across my chono and I found that of the factory ammo I tested, only the Federal ammo lived up to its claimed velocity. Rem and Win were both 100fps slower than claimed. I also tested some of a friends Sellier and Bellot ammo and found that it was 200fps slower than claimed with the brass being brittle also.
Good luck and good shooting. I guess I'd go with the 300WSM also. save your brass, you may not handload now but you will.
Of the three you listed, go with the 300wsm if you don't handload (even if you did from those 3 choices I would go with the 300wsm). But for what you want to do, I would look hard at the .260 Remington. Great for antelope and deer, and with some well constructed bullets elk within 500yards (or further) are in range. 7-08 or just a .308win wouldn't be bad either. I just think a .260 would be ideal for what you want to do with factory loads.
I think the 270 WSM is an awesome cartridge, however I agree that you should look into the 7 Rem Mag. The Tikka is a fine rifle but in my opinion if you get a Rem 700 you can build onto it and customize it better as you go.
My .02 worth is,, go with the 300wsm, lots of good ammo available and as far as rifles don't overlook the savage line. I have 3 and all shot sub-moa right out of the box with factory ammo.
They are also very user friendly to customize down the road if you wish and the accu-trigger is nice too.
I would go with a 7mm Rem Mag. Been around forever and large selection of factory ammo that will make it easier to find ammo your gun will shoot well. If you decide to hanload down the road it is even better. For factory ammo you need to go with a cartride that is popular. Look online and on tje shelf in stores and research which offers the best selection that is readily available. There is no guarantee a factory rifle will shoot the ammo you pick well so the larger selection the better to insure you can find somethng that will shoot. Savage and Howa/Weatherby Vanguard are my two favorites for a factory rifle that will shoot right out of the box.Remington used to be my number one but now has moved slightly below savage and Howa/Weatherby Vanguard for out of the box accuracy. All three offer excellent paths to customize down the road. I also like the 7mm Rem Mag over the short mags in a factory gun is the long action mag bolt face offers the ability to rebarrel to many more options than a short action which still gives you the option to rebarrel to a shortmag down the road if you decide to. Chances are you will decide later to handload so leave your options open. If not then you will have the best Factory gun/ammo combination. Thats my 2 cents.
I'm by no means a ballistics guru. So if I'm just shooting factory loads, does the 300wsm simply offer a little more down range energy over the 270wsm? With the velocity edge going to the .270wsm?
Another thing, I don't forsee ever needing to utilize a 180gr bullet.
Just some additonal thoughts.
For years I hunted with a 7 RM and when I burned the barrel out and went looking for another rifle, I decide to go bigger, not smaller. The 7 RM worked very well for me but I wanted a little more killing power for insurance, especially where elk was concerned. the 270 WSM should make a good hunting rifle. The 300 WSM will be a little better killer.
Winchester shows the 270 WSM 130 E-Tip @ 3275 fps and the 300 WSM 180 E-Tip @ 3010 fps, which are going to be fairly accurate velocities. The 180 E-Tip will maintain a 400 ftlb of energy advantage over the 130 E-Tip out to 600 yds.
If you get the 270 WSM, I'm sure you'll like, but someday you might have wished you got the 300. Just giving you my experience and opinion.
Most important is the rifle you choose. I really, really recommend the Weatherby Vanguard Sub MOA. Did I mention that I recommended the Sub MOA Vanuard? The Savage guys like their Savages and that would probably work too, but I like the Vanguard action a little better and they have a quality pillar bedded stock.