Between the .280 AI and .300 Win Mag, I'd go with the .300 Win Mag loaded with the heaviest bullet/highest BC that your rifle shoots accurately.
The .280 AI can equal or close to the 7MM Mag performance, some might even exceed it. My hunting buddy has a Wby MKV in 7MM Mag and wants to get a .300 Win Mag for elk. He doesn't reload or have any desire to. He max range is 500 yards. I told him his rifle has plenty of energy for his intended purpose and I use the chart below (with the exception of the .270 AI, all factory load data).
My unwritten rule is 1500 FT-LBS of energy and 1800 FPS minimum at target impact for elk ... but shot placement is still the key.
Look at Jeff's (BROZ) posts about his .300 Win Mag successes with the Berger 210, 215, and 230. Hopefully he'll chime in.
I voted for my "FREEDOM", "GUNS", and "MONEY" - keep the change - UNK.
"I am always proud of my country!"
"Leadership Rule #2: Don't be an edited." - Maj Gen Burton Field.