I'd say that Art pretty much got it right. I sure wouldn't worry about the "little" .243's ability to drop a deer. Only suggestion I would make regarding shot placement that has not already been mentioned would be this... If the deer is looking directly at you, aim for the white patch on the throat directly under the chin. It makes a great target and any hit slightly high or low will drop the animal like a bad habit. (If the animal is facing you but not looking up, just give a little whistle or grunt, it will look up.)
Hope you have a great hunt!