Here is my new sharps I recently picked up from prophet River an 1875 c Sharps in 45/70.Suprisingly for a heavy tapered barrel it carries and balances quite well for hunting.I ve replaced the front sight with a blade for hunting.

To answer your question: Yes....both the Pedersoli Sharps, and Rolling Block rifles are capable of handling modern, 45-70 ammo. Within limits. .
I will be at first buying handloads from a british guy named Peter that a lot of Nova Scotia gunnutz probably know. Then once I have a supply of brass I will start to loading them on my own. His Cowboy action loads are top quality. I really like that officers model but the price is so much more then the standard one. It might be worth thinking about saving longer.
I can keep it within reasonable limits. I am currently a handloader, (.308 win, 300 RUM, .416 Rigby and .458 Win mag). I would likely later want the stronger one though. I am still on the fence.
I am starting to lean this way, or I will eventually end up with both. I watched some Hikok45 vids and the rolling block looks pretty good too.
I am buying it to use, I know this might sound weird but if I had an original I would be reluctant to take it out and enjoy it for fear of ruining it. A reproduction I will be able to freely enjoy.
Here's how I decided.
I've also found the Rolling Block rifles to be more accurate, but that's likely because I don't have to search to find the sights.
Chasseur: I too, am an admirer of the clean, simple lines of the 1875 Sharps. I've had one of these on my radar, for some time. Please do keep us informed as to your adventures, with this fine, C. Sharps.
Nobody here a fan of the Ballard family of rifles? There was a lot of good shooting done with them back in the day.
I missed out on one on the EE a while back.