.50 is for fun.
.58 is for harvesting. Go with a Minie gun and reach out, reach out and touch something at up to 500 yards.
OK, if you're dead set on a Plains type rifle and will be using it for hunting, go with .54. Not as available but bigger balls do more damage.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!