eeshooter,
You are going to hear a lot of different opinions about this and that caliber, and it may be a tad confusing, especially since a majority of them will be in .22 caliber.
Have you ever fired at that range? 450 yards I mean? A prairie dog is a might small target even at 100 yards - much less at 300 to 400 yards. The wind will play hob with your bullet as it gets out there also, but maybe you have experience with long range shooting.
At any rate, if you want 'lightning-stroke' killing shock out that far, you should lean towards one of the bigger rounds like the Swift or one of the newer big boys like a Lazzaroni. That will let you have all the velocity and also reduce the windage and elevation error's at range.
But I don't think that you should overlook the 22-250, or the .222 Rem for that matter. In fact, a 'trip-deuce' is an excellant performer right out of the box.
Good Luck, U.G.