Of the calibers you mentioned I would choose the 280. I've been using on for years and I reload for this caliber. This year Federal has introduced several new loads and Hornady also has a new load out. This makes the 280 better than ever in my opinion. I guess it has become popular enough that even the local Wal-Mart carries core-lokt ammo for it now. The 280 is right on the heals of the 7MM and out to 300 yards you and any animal won't know the difference. The A-Bolt is a good rifle and is pretty light compared to a Remington or Winchester. All of the calibers you listed will work well I just am partial to the 280. If you choose the 280 I would look to the 140 gr. loads for your type of hunting. As I stated I reload but I have shot factory ammo in my gun. My best factory ammo load is the Winchester 140 gr. Ballistic Silver Tip. This ammo will consistenly group under an inch out of my rifle. In a pinch for deer hunting this would be the factory ammo I would go to. Also, if you ever get a chance at elk Federal has a 160 gr. Accubond load now available that could be just what the Dr. ordered. Good luck on your decision and purchase. Don't be influenced too much by everyone's opinion as you're the one that has to live with your purchase.