Caliber Decisions

After much consideration I have determined that I am really in the need for a large caliber hunting rifle. With this epiphany, the decision of which caliber and cartridge to choose has resulted in some serious research. I am looking for opinions and commentary...

Do you think this one might be too excessive?

For comparison purposes the small round is the standard 5.56, the projectile is a standard 20mm M55A3 and the squares are quarter-inch scale...