In my opinion bullet weight and the energy behind the bullet are the best factors when considering personal defence. However those can also have a significant impact on accuracy as well.
I saw a rifle on TV here a few days ago that shoots a 6.80 round which shares the "knock down" power of the 7.62 with the accuracy of the 5.56. Seems pretty cool, but I would guess it's really all a matter of personal opinion.
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