Well, a turn-of-the-century English best, seeing seasonal use, with black powder or equvalent English period loads, gone through every season by the maker, should last a long time.
But, sometimes, they don't. Sorry to pop the bubble. The notion they are all still in use is a foolish one, perpetrated by fools, that persists in spite of evidence otherwise.
For my money (cliché, I understand, but, IT'S MY MONEY) an English (sorry, only those English guns with modern levels of proof need apply) or continental boxlock on the Anson and Dealey patent, with disc set strikers, and perhaps intercepting sears, if we want to impress the "conoscentí", will prove to be more durable and capable than most of us.
For a great price.
Best is as best does.
Best,
Ted