I'm for long barrels as well. I was considering getting cheeky and saying that a barrel should definitely reach all the way from the breech clear out to the muzzle.
But I thought better of it......
In my case, that's at the lengthy end of the range among my flinters. My shortest is 42" (.54), then 44" (.25 and 20 ga), 46" (.50 smoothrifle), and a 48" (.50 rifled). I just got a Rice A-wt .40 that's 46" and not in a stock yet.
I used to shoot pretty short barrels (all under 34"), but find them hard to hold and funny looking now that I've acquired a taste for length. It took a while to get over that modern cartridge rifle esthetic, but that passed about 30 years ago.
Bottom line: you can always shorten, but it's tough to put it back once hacked off.