I've taken a deer and several hogs with the .223 using 55 grain TSXs. They seem to work as well as anything else I've shot them with. One went through both shoulder blades on a hog, a shot I've seen stop a Remington 405 grain SP out of a 45/70.
I do find myself waiting for an ideal shot with the .223 when I'd take a shot requiring more penetration with a .260 or up.
(I've not shot anything with a .243, so I can't comment on it.)
