OP,
Here is a link to a story about a hunter who killed a 390+ bull elk at better than 500 yards using a .257 Wby Mag:
http://www.hightopoutfitters.com/for...php?f=22&t=175 There was nothing unethical about this hunter's ability to kill an authentic trophy with a cartridge that some might opine as inferior.
The point of this link is that you might not need to step up from your .270 Winchester. The .257 Wby Mag is an excellent cartridge, but then again, so is the .270 Win.
There is more to choosing a big game rifle than a cursory look at ballistic tables. I prefer bullet momentum to velocity. I prefer to look at impact velocity rather than muzzle velocity. But none of it matters if I'm unable to place a bullet where it needs to be.
99% of the time I won't say a word about what rifle another hunter uses. Many hunters would be quick to dismiss a 120 grain bullet fired from a .257 Wby as ineffective elk medicine. The bull in the photo found at the link didn't think it was ineffective.
Keep in mind that biological science and not emotion controls our sport. If you can destroy an animal's heart and/or lungs, it will die. And it won't go far before dying.
I'll leave you with the following. Forty years ago, when I took up the sport of big game hunting, I bought a Model 700 .270 Win. Later, when I wanted to hunt elk, I bought a 7MM Rem Mag because it was the definitive elk cartridge. I must of been a lot smarter than than I am now. If I were accorded a life do-over, I'd buy only one big game rifle: a good quality .280 Rem & hunt everything with it and never look back. But that is me. You'll have to do what's right for you.