I'm a 300 Weatherby guy for elk these days using it instead of my slightly more accurate 7mm Remington Mag because I want the extra down range horsepower. I hunt primarily wide open spaces but also in the trees, many of my spots are very near some private ranch boundaries so stopping them quickly is more important to me than too a lot of hunters.
Either of your rifles will kill elk just fine - I'd go with my favorite based on the way I felt. I think a light 270 Weatherby is a very cool elk rifle and I'd carry one in a minute. I got an elk to do a backflip at 550 yards with my 300 and I see a difference but I've also had a small cow absorb one from 100 yards with no reaction even though it jellied her lugs and pulverized her off side shoulder. Unless you interrupt the CNS stopping elk is a lot harder than killing them.
If I were going to build a 2 rifle elk battery I'd probably go with a really light fast 270 for extended hikes and a kind of heavy fast 338 for less mobile hunts. I'm right in the middle with the 300 Bee for my one rifle set-up and think it is just fine but it took a while to get comfortable with the change.
The only trouble with the .300 mags (I'm going to group them, the differences are small) is that your turn at the campfire cartridge debate is very short. Those with smaller get to argue that theirs are good enough, or just as good or kick less, but few will argue that a .300 isn't a first class choice for just about everything, just about everywhere.
