If by “big game” you mean deer, The 30 Remington AR has enough energy for deer out to 300, and with the right load you could probably take elk at 200. If you plan to regularly use this gun for elk, bears, moose, etc at 200 yards, you may as well stay with your 270. But if I had to pick an option you listed, the 7-08 with 140gr Accubond or TTSX
