When you get tired of crippling birds, you'll probably end up shooting #2 or #1s. #4 are best for close up shots, they run out of steam pretty quick. Back in the days of lead #4 was plenty and some hybredized heavys it probably still is but, in plain steel I would go with #1 and maybe #2 if you can get them to pattern out to that distance and penetrate. It doesn't matter how fast they leave the muzzle, if they can't penetrate when they get there it's pointless and will only increase crippling rates..
Save a Salmonid, shoot a sawbill