deer size is relative in my book, as far as 223 being suitable.
On Vancouver Island, of the coast of BC, They have these deer that are about the size of a golden retriever, and a mans big game hunting gun there could EASILY be a .223. I doubt those deer weight more then 60-70 lbs.
Go east a tick over to Saskatchewan, and there are bucks there that mooch off the wheat fields that I would really REALLY have second thoughts about going after with a .243, there quite sizable deer.
So depends on the size of the deer, I'd say.