I have both, and like both, but prefer the .54. Assuming you are considering the same rifle that is available in both calibers (Lyman GPRs in my case for both rifles) the larger caliber will have the bigger bore, ie, less metal, so will be slightly lighter in weight. It will also use slightly more powder and lead, so there is a trade off. Speaking of powder and lead, it is often said that a .50 will shoot flatter than a .54, or a .45 flatter than a .50, etc, etc. I call BS on that one IF equal loads are used. Notice I didn't say equal powder charges tho. If I limit my loads in my .54 to the same 70grs FFFg that I use in my .50, then yes, the .50 will shoot flatter, but that is because it will be traveling faster so we are NOT getting a true comparison. To get a true comparison, we need to start both caliber RBs at the same velocity to start out with, which will require more powder in the larger caliber to start out with. If you start out with equal velocities, then you will see that the larger caliber actually maintains it's velocity a little better to in truth shoots a little flatter. Now it won't be a lot flatter, so please don't misunderstand me, but it will be a bit of an improvement. But like I said earlier, you will pay for that flatter trajectory with more powder amd slightly more recoil. I would still get the larger caliber considering the game you mentioned, because it is always easier to load a larger gun down than it is to load a smaller gun up.