OK the standard that has been held up for determining if a round is good for whitetail deer has been will it produce over 1000 ft lbs of energy at the range the animal is shot from. I also sometimes see 800 ft lbs held out as the standard. Sectional Density should also be north of .200 for a hunting bullet.
The advice from anyone holding out energy as a barometer for killing with a centerfire rifle cartridge can easily be ignored. Sectional density seals the deal.
Factors, in order:
1. Shot placement
2. Bullet integrity
...
100. Everything else
The surest way to drop the ball with #1 is to talk a shooter into a boomer under the guise of more energy mitigating misses. The surest way to gloss #2 is to talk headstamps as if all bullets are the same, or in SD as if all of the same weight and bore size are equal.