I really like both the .25 and .270 cals for killing deer, one of my favorite is a 250AI and I would think the 257WBY would 300-400fps better. I also shoot a 270 WSM which will smoke them out there also, I am easily pushing the 110TTSX at 3670 fps, recoil is so mild it almost funny.
Running some ballistic cals, they are close but you can get the 270 WSM to do more with the wider range of bullets that will work for deer at longer range. The 110 TTSX will top out at 800 yrds but you can load 130 Bergers to 169.5 Wildcats for it also maybe giving you more wiggle room. You may have to be more careful with the 257 WBY bullet choices.
I would assume the 257WBY would be harder on barrels.
In short it's a toss up for me, but I prefer the 270WSM
The ideal solution is one of each!!!