It would completely penetrate the deer. Might not cause alot of hydrostatic shock. But what a 12ga has going for it is diameter. So it would cause a big hole around .6".

Energy and penetration does go hand in hand, if you keep all things static except one. If you had a infinately hard bullet, that deformes 0, and the medium struck is static and stays the same each time shot, then yes energy goes hand in hand with penetration. But then you got to consider momentum. Or moment of the object. A 200gr bullet with the same energy as a 25gr bullet with velocity varying, will not penetrate the exact same.

The problem is each bullet deforms (most of purpose) differently, including different slugs. There are different hardness of the lead, and bonding of the material. So its hard to understand you question. As far as damage, there are different things that cause trauma. Hydrostatic shock, (more speed, more shock), bullet diameter or cutting surface (bigger hole bigger bullet).