TheHungryHunter said:
"...killing power between the 50cal and the 54..."
Just seeing this post, while the wording is a little subjective, IMO a .54cal PRB has more 'killing power' than any smaller, lighter PRB. As I experimented with .45/.50/.54/.58/.62cals for deer hunting over the years, I saw first hand the difference in 'killing power' as the balls grew larger, and as the PRBs grew larger that also extended the effective range some each time.
As an aside, when I made the step to a .58cal, the jump in power was significant and very noticeable, making me refer to it as having "whompability"...and when I decided to start thining the herd and settle on a long rifle for big game hunting, I had an early Virginia built in .58cal...never a question about the outcome at any angle or any distance that I'd take a shot at big game with a Flintlock.
In that same vein, if my only choices for a single big game caliber PRB were between a .50 and .54cal, without hesitation it would be the .54cal...others mileage may vary.