I have a couple .58 rifled muskets, a Pedersoli Cook and Brother Carbine and a Zoli Remington Contract Rifle. Both will shoot Minies or round balls well. Love the carbine for hunting. Light to carry and quick to bring on target.
The way I see it it isn't a matter of either/or, but a case of the more the merrier. Lots of projectiles and molds out there for the .58, because there are so many guns in that caliber. If it is not the most prevalent caliber, I'm guessing it has to be the second most, what with all of the War Of Northern Aggression style arms out there. So there has probably been as much or more load development and experimentation as with any other caliber as well.
Yes you are going to use more lead per projectile, but seeing as none of us are headed to Gettysburg or into the Rockies for a season, I can't see the amount being carried as adding that much weight to your kit.
As far as powder, mine shoot well with as little as 40-50 grains, and the service load was around 70 grains. The larger projectile provides plenty of punch and gives you a lot of flexibility.