I have seen slow twist barrels shoot sabots, conicals, almost anything. Then the next slow twist barrel will only shoot roundball. Only your rifle knows what it wants to shoot. While I am sure a well placed roundball at a moderate range could kill an elk, I tend to agree with you on the bigger is better theory.

Since the barrels are the same on the Great Plains Rifle and Great Plains Hunter, I think I would get a .54 caliber Great Plains Hunter barrel with the 1-32 twist. It should fit right on your stock just fine. From there I would work up a .54 caliber conical load with as heavy a powder charge which still produced accuracy. A lot of people with the GPH barrels shoot the Lyman Maxiball with excellent results.

Another option would be the Green Mountain Barrel from Track of the Wolf. They come in a 1-28 twist that would be good for conicals most likely, and sabots. If sabots are legal. Most Traditional Hunts do not allow the use of sabots. While a 1-28 twist should shoot conicals, it is no guarantee that it will. They really are made for sabots, as they are basically the same barrel you would find on a Knight rifle. I personally think for big lead, I would go with another GPH barrel from Midway USA and work up a conical load.

A large conical, while not having the speed of the sabots, have energy. They have excellent penetration and expansion and might actually be a real good choice. I have never had the pleasure of hunting elk with a muzzleloader yet. When I do, it will be with a conical shooter.