1. You are going to some fine, fine, pronghorn country. I am a little jealous.
2. Pronghorn are not hard to kill. Any of the cartridges you suggest have the range and power to kill antelope.
3. As we all know, shot placement is more important than terminal ballistics (ignoring unreasonable extremes). Therefore, if the Creedmoor is not as accurate, then that is the easy one to rule out.
4. Since we are talking pronghorn, which are just not that tough to kill, I would recommend the one with less recoil, which, in two rifles which weigh the same, I believe would be the 270 WSM. Which is plenty, PLENTY, of power for pronghorn.
Is there a rifle or a scope that you just like a little better? Maybe go with that one.
Sounds like there really are no bad choices here. Whichever one you pick, don't fret over it too much. You will have more than enough gun.
(Besides, your rifle will jam and you will end up borrowing your buddy's rifle, and you will STILL do fine.). ;-)