I would ditch the ft/lbs analogy and rely on common sense, and the experience of others.
Personally, I would hunt elk (or moose) with a .308 Winchester and a 150gr TTSX before I would hunt them with a .300 Weatherby and a 180gr Ballistic Tip, even though one has more energy. With elk penetration is key.
Pick a good cartridge (.270 Win/7mm-08 and up) and a good bullet (partition, accubond, (T)TSX, GMX, E-Tip)and shoot out til the velocity starts dropping below 1900fps.
Put a hole through the lungs and you'll eat tenderloins.
