When you buy into a a super magnum you are in reality buying it for extending your range. Same bullet going faster = more range. It's not about energy... The bullet design dictates its terminal performance for it's given intended speed range. Keep the bullet in that range for best terminal performance on game and then it's all on you to put it at the right spot.6.5-300 Weatherby.... it's noticeably flatter shooting than both rounds you're considering, and with 140gr bullets carries plenty of energy to 600yds.
Not saying that the 6.5-300 Wby is not awesome because it is...! Just thinking that it is a bit much for under 600 yard hunting. Too much meat damage when used up close unless you use mono bullets like the Barne's or Hammer's.