I think it depends on whether you are hunting wild birds or pen raised too.....

For Blues we use 12 ga. 6s....they are wild and get up at 20 or more yards regardless of what kind of dogs you have.....

I've been working my GSPs every day (without a gun).....today my 10 month old pups both went on point.......I walked over and the quail got up 30 yards from me......

Blues have a feather pattern that prevents small shot from penetrating at a distance......some of the guys use 7 1/2s but they lose or cripple a lot of birds.....

Most of the guys I hunt with also use high brass loads......
and we do kill a lot of birds each season.....last year over a two day weekend 12 of us killed 287 blues.......it's not unusual to kill 100 in a day.