I have a 700ml in the safe, a .54 stainless in excellent almost NIB condition, which I may convert at some point to a Brux .45
While the Brux 45 will be a joy to shoot, you should at least consider the Hunter smoker kit for the 54cal. It would make an absolute hammer with BH209, MMP54x50 sabots and the 385gr Rem CLHP. It would easily equal a 50Beowulf in fps with the same bullet.