Jeff, sorry tot ake so long to respond, some #$%^&*( lowlife virused our computers and it's taken this long to get back up.
Shotgun stocks are longer because they're pointed,not aimed, on flying/running targets. The length aids the swing and lead. Rifles are aimed,and a shorter stock is in order to better acquire the sights.
For our purposes, there's leeway. For HD and general shooting, the standard stock of roughly 14 1/4" pull fits the mythical average guy of 5'9", medium build. I'm 6'2", heavy build,and shoot the standard stock well enough. I can also do acceptable work with the 13 1/2" Youth stock if I have to, tho the standard does work better with me.
For wingshooting, many folks would do better with a longer,straighter stock. On my bird 870, I've shimmed the stock a bit to reduce the drop about 1/4", which doesn't sound like much but moves the pattern maybe a foot at 25 yards.A longer recoil pad added a bit to the length, giving about a 14 1/2" pull.