I want to rebarrel an old 270 post 64 model 70 of mine. The barrel is in tough shape. I'd like enough punch to take elk to 700 yards or so if I ever get the opportunity. What would be the best performing deer and elk cartridge for this project? I was thinking 284 Win or 280 AI. My only requirement is that they feed well and I've read about feeding issues with both of these chamberings. Thanks for any advice.