I have found a whole deer skeleton in the woods with the lower jaw shot away (no, it wasn't dragged away by another wild animal). No doubt the hunter had been going for a 'central nervous system shot'. The brain in the deer family makes an especially small target, and this is especially true in a moving animal. The spinal cord, the diameter of your pinky, makes an even less attractive target. You are far more likely to hit neck muscle and simply injure the animal. Again, the latter is especially true for a moving animal. I am not challenging anyones hunting prowess but I think the 'central nervous system' shot is unfair to the deer. I know you know this already, but the hunters job is to kill the animal as quickly and cleanly as possible. This is why a chest/heart shot is a much better target. The sheer size makes small errors forgivable.
There is nothing magical about .30 cal. If you are concerned about brush you can use a partition bullet. If this is less a concern, then a ballistic tip or soft point. You must have adequate penetration/expansion/fragmentation to tear as much lung tissue/blood vessels as possible so the animal has no breath and no circulating blood. If it hits the heart that's great too. These are what make an animal collapse.
Even with a properly expanding bullet, .223 is simply going to damage much less tissue than a larger diameter bullet. Less tissue damage = deer runs longer. On a 200 lb. animal, is that something you want to risk? I grew up in Ontario and so I'm familiar with the weather, general topography (variety) and flora/fauna. I can't imagine anything more frustrating than tracking a large deer with a .223 chest shot,in thick brush, with a light drizzle slowly washing away the blood trail.