I've shot a .257 and .270 Weatherbys in the past and didn't notice much if a difference in the recoil between them. If I were in your shoes and already had a .257 I would get the .270 so you have another Weatherby caliber in your collection.
Just be aware that if you get a 270Wby, it may well steal your heart. Mine did. I bought it fully expecting to have it rebarreled to 257. That changed after reading a load manual, and was cemented after the first range session. Taking my first deer with it years ago absolutely stole my heart for sure.
About ten years ago I bought my Dad a custom Euromark in .270 Weatherby Magnum and that caliber is absolutely amazing, super accurate and he's never had to fire a second shot to kill anything. I'd say it's kinda like a .257 on steroids.