RE: 45/70's
First, remember that a Sharps action isnt as strong as a Ruger #1, modern bolt actions or a Marlin lever action. You want to be careful what you feed it.
Having said that, if a Sharps 45-70 could take bison...I reckon it still can. Big heavy bullets dont stop real easily. Dunno I would try it on blue whales, but anything that walks would be fair game.