Kirk Bryan, owner of Shiloh Rifle Company, has publicly stated that his Shiloh 1874 Sharps' rifles will handle any load that a Ruger #1 can tolerate. I doubt that he would make such a statement if it wasn't correct. I certainly would NOT trust any other maker's Sharps' rifles unless they too made a similar statement.
I have a Shiloh in .45-70, and it has happily digested many loads which are far warmer than "blackpowder equivalent" levels. Mind you, it's not very comfortable to shoot with real hell-benders, being of standard sporter configuration and mounting a tang sight which makes it difficult to get a good grip with the trigger hand.
At about 1500fps with 400-grain bullets, it offers a good bit more power than most factory .45-70 loads, and is still pretty comfy on the back end. NICE rifles, the Shilohs!