I used to use 7 1/2 or even 8's for ruffed grouse when the leaves were all on the trees. As the leaves fell, I'd go to 7 1/2's or 6's, and when the leaves were all gone, 6's.
I must say, for a while, in the very early season, I used 9's, and they worked fine. Grouse aren't hard to kill.
My loads were all relatively mild 20 gauge loads, like a skeet load (no joke intended).
In ruffed grouse cover, especially early, most of your kills will be pretty close- if they get 30-35 yards away, they are out of sight. Once the leaves are down, longer shots can happen.