If thats your choice's flip a coin. I would change the 270 and 257 a 7msm and 300msm or old school mags like 7mmRM or 300wm. The 257 is a barrel burner literaly. Short life span and much more a speed goat cartdge. the 270 does nothing a 7mm won't do with more energy on target. Both pack a bit more punch for ether mulles and elk.
I would vote for the 270 wsm. I've never shot the 257, but I really like the wsm. I know ppl that use them for elk with no problems. I have only shot it myself a couple times but really have liked it. I own the 300wsm and it is my favorite large caliber rifle.
The .270 WSM. The .257 is not intended for elk sized game. Yes with 120 gr partitions it will do, but the .270 should be better. I agree the 7mm is better yet as there is a wider range of bullets available to the handloader. 175 gr Partitions are the bomb on larger game.