The whole idea of shooting something is to put a hole in it.
7.62 is heavier and will make bigger holes. The whole discussion of hitting on subsequent shots is just that - another discussion.
Well then a cannon would be better by that logic.
The projectile’s velocity plays a big part in the quality of those holes. Spritzer bullets tumble upon impact at velocities exceeding about 2400 FPS. 7.62x39 exceeds that mark by very little, at the muzzle. Bullet construction accounts for some of the damage done, as well. I think I recall that one of the characteristics the Army was looking for when they adopted the 5.56 was that it be supersonic at 1000 yards.
The author’s question has already been answered by the world’s militaries: 30 caliber for intermediate range. 7.62x51 or 7.62x54. We use AR-10 based rifles (and Remington 700’s in the past), Russians use the SVD Dragunov.