Being fair to distanced, I have used, and killed more game with my .222/12 guage over/under than any other rifle I have, or will ever use for that matter....I have never lost 1 animal, nor have they run...
Shot placement is paramount though....
I wouldn't try a moose with it, and I personally like the smaller calibers that do just as good as the much larger ones...You must consider the type enviroment you'll be hunting, if it's wooded, brushy, and thick, a heavy caliber should be thought of first....If it's a bit more open and allows you a longer, and cleaner shot...I lean towards the 6mm Mag.
I personally love mine...Hunt deer with it in the fall, and burn groundhogs up with it in the summer, the only thing I do is switch from my Leupold(Deer) to my 20X Jurntal(Groundhogs) with spring action precussion mounts....Of course I played around with it a bit...Bedded, free-floated, trigger re-worked, and removed all the factory ejectors and extractors and replaced them with Sako.....
Hmmmmmmmmm......Did I say Sako...???
Now there is another thought....<evil wink>
Ranger