I limit my use of #9s to skeet, for which it is well suited. I prefer 8s for grouse, woodcock and quail - it is a little more versatile. For those birds, you are not giving up much in the way of pattern density on the close shots, but get better results on the longer second shots. I suppose you could mix loads in the R and L barrels, but I haven't seen a reason to do that for the hunting I do.
Back in my youth when I lived in state that had dove seasons, it was all 8s and 7.5s. I don't recall ever using 9s - but that was open field shooting with few incomers like at the waterholes.
RST has been selling a #10 Woodcock load - it must work but that seems kinda light to me.
