RE: 400 yard trophy?
It would be backstraps on the grill that evening and a trophy on my wall.
This is a no-brainer.
Gun of choice would be my Browning A-Bolt 7mm Rem Mag with a handload of Nosler 140gr Accubonds.
But then again, my buddies and I all handload all our ammo, and we place 20 ounce pop bottles filled with water at 300, 350, 400 yards and kick back an bust 'em shooting off our backpacks for fun.
To all those who said to stalk closer you obviously haven't hunted flat-open country or out West.