DonD,
A hunter ought to know about the physical structures of the animal, the capability of his load and bullet with regard to those structures, and how it affects bullet placement.
Bullet selection is more important than caliber for calibers that are more or less close in bullet mass. A varmint bullet in 257 Roberts +P is going to blow up just like a varmint bullet in 223, and a stoutly constructed bullet in either caliber will get more appropriate penetration. (For dramatically heavier bullets, I think you can get away with less careful bullet selection, because chances are good a 190gr or 300gr SMK is going to truck through an antelope or deer just fine.)
Based on some results posted last season by others, and my testing into a tougher medium than bone/muscle (and observing the LACK OF jacket separation/fragmentation), I would have no qualms using the 70gr TSX on deer, for the type of close range hunting that is typical in the midwest and East. There is no other bullet I would try with confidence in 223 right now. I have not yet used any 223 loads on deer. (The next bullet I have in line is the 110gr TSX in 6.8SPC.)
For reference, my experience is with my family hunting deer in Wisconsin using 30-30, 257 Roberts +P, 270WIN, 30-06, 7mm Mauser, and 6.8SPC.
-z