My quick answer would be that almost nothing compares to corn when the Snow is more than 12" deep and carbohydrate stores mean everything for survival and going into spring "fattened up" for birthing and antler growth.

Being that you are in the south, I cannot knowledgably comment on how corn compares in the the winter months to say....brassicas or fall planted Rye/Wheat.

I'm sure you know that corn stinks from a nutritional standpoint (I mean protein) - but excels as a carbohydrate source.

I guess I'd sum up my thoughts that if your deer herd is stressed in the months that corn matures, dries, and dies off - the ears can be a real good source of energy. Corn before it heads out, and/or when its immature does very little for deer.