Not sure where this "long belief" comes from exactly. I've read 1200 ft lbs minimum for elk. I've read 800-900 ft lbs. for deer. I suspect that it could be done efficiently and humanely with a lot less than that if you're careful about where you put your bullet. I know deer get harvested here in Texasquite regularly using a .223, which only has about 900 ft lbs at 100 yards...