i say just go with the 54
you can always load down OR up
i have two 54 cal. and like has been said earlier 32-34" barrel,, both of mine have 34"---1-60 twist round ball barrels,,
.530" patched round ball and 60gr ff goex,,,if used correctly and put in the boiler room will take any white tail you will ever shoot at,,,,i have never not had the ball to pass through the rib and lung kill zone,,,40 yrds through 120 yrds never failed yet to pass through
for the bigger stuff i move the load up to 80gr ff goex
i don't get this conical plastic sabo sh--....stuff,,,,and pellet powder WTFE
the first thing you want to do when you pick your rifle is get it shooting,,,muzzleloaders are just like center fires there will be a magic load that will work with your ball or bullet combo,,,seek it out,,,that is where lose powder shines,,,
i can tell you from experiance with a 54 you will never need a heavy load for a white tail deer,,,,if your rifle you buy likes and shoots accurately 50-70gr of powder with the bullet you choose,,,you will have a winner and a deer killer
put it on paper and get it shooting first,,,,the deer deserve your best shot,,,and you deserve the right to say ,,,one shot - one kill
my .02
ocharry