I think the question becomes irrelevant when you get hit by a bullet of any caliber.
People argue the stopping power/lethality of 5.56x45 and 7.62x39 all day.
What is generally recognized is 5.56 is more accurate but US troops have always been reporting that even if they hit a target with a 5.56 round, he tends to get up and walk away (how far he gets is a different matter).
7.62 within effective range tends to just blow a hole right through the target, delivering more kinetic energy per square inch through the torso, than 5.56 which tends to go into an axis spin and fragment upon entering the body.
Stopping power, in this discussion, can be defined as the kinetic energy delivered to the REAR of the target, just before the round exits the body. 5.56 on average tends to deliver less kinetic energy to the rear of the target than 7.62.
As I said at the top, thats all irrelevant when you get hit by either.
Without immediate medical treatment, a shot to the abdomen by a 7.62 or 5.56 (or .22LR) will kill you within 4 days once your intestinal tract is punctured.
This stopping power crap can be debated all day in the ivory towers of the internet forums, but the dimensions of the bullet are irrelevant when they are flying past your face.
edit: I rarely go hunting but when I do, I find the animal (deer, hog) is only flattened when using .30-06 or .308. We have used .270s and the animals tended to get shocked to the ground then immediately get up and flee. It didnt get very far but it still got up after it was hit. For hunters, you probably know that the animal fleeing isn't good, since the fleeing results in lactic acid spreading through the meat and making it less tasty.