Confidence in your equipment makes for good shot placement. Shot placement is key. I have shot many elk. Most with my 7rem mag. One was well past 300 closer to 350. I shot that one with a 243 and an 80gr bullet. I have watched them get shot with 243 all the way to 300 rum and if the shot is true they all expired quickly. But an off shot even with a rum wont end well. A 280 is adequate for the range you are expecting to shoot. But there really is no such thing as overkill because there is no such thing as overdead.
Plus 1. My experience has been that confidence makes for success. My brother shot a huge 6x6 at 620 yds with his 280 and a 150 partition. He had never seen a ballistic table, but he knew where his gun shot at 600. He used a browning with a boss and a 21 1/2" bbl. He didn't know that his muzzle velocity was more like a 7-08. He hit the bull, and it laid down more than dropped. It was dead when he got to it. He never suspected that he had anything less than a great elk gun. Now that he knows it is a 7-08, he uses his 300 saum. Pick the caliber that you have confidence in. It will work for you.