I was somewhat surprised and delighted to see your inclusion of the .50/70 in the list of possibilities.
I played with one, a single shot Sharps, 1868, for a while. Accurate Arms, now Western Powders had data at that time using AA2015 powder pushing the 450gr. Lyman bullet at 1,800 fps.
At the time I daydreamed of such a ctg. In a DR made on a good shotgun action.
My current model 1876 Winch in .50/95 drives a 368gr. FN Lyman bullet at 1,650fps. I am sure it will "answer" for anything I need it for. The .50/70 will easily match that, I am sure with a variety of loads.