I have posted many times about my go to round. The 168 Berger going 3067fps from my Browning A-bolt. The same round works best on coyotes too. The 22-250 is not as good but is maybe safer and quieter in the country side. My best gun to carry is the 243wssm with 55gr going 4060fps, down side is the report, its loud. The Z5 maybe the reason I like shooting it best. The 7mm has a VX-7 which is really good but not as easy to get along with as the Z5.
Instead of which gun, maybe the scope plays as much or more a part in what works in the field. The Nikon on my 22-250 is not as much to my liking. I have never owned a 270, probably never will, not anything against the 270. I just don't have the need for it. Its too close to the 7rm which has an advantage due to the amazing ammo available. Anyway if you make a choice of any of the rounds listed in this post, it will be fine. I am looking at that 280, sounds good so far.