RE: whats the difference?
You can kill any deer built with a 22 rimfire or a sharp stick, the trick is to be effective with your method. A 222 will kill a whitetail quite effectively, but don't expect an exit wound. A gut shot will probably be a lost deer. There will be very little blood to track with. A shot on the point of the shoulder that has to go through bone might not be as effective as you would like. Light bullet construction means you will have to shoot appropriotly.
All that being said, shoot the 222 like you were shooting a bow, right behind the shoulder he will die, now you will have to make the call of can you find him or not. Same with 223.
My theory is shoot the biggest gun available, that you can shoot comfortably. Too dead has never been a problem for me, but not dead enough has. The reason that some states do not allow smaller calibers is the simple fact that many people are not responsible enough to pick there shot and game is wasted when they wound and loose the animal.
The question is not will the 222 kill a deer cleanly, but do you feel comfortable going the extra mile to make it happen.