I am not a fan of the GD stance at all. All the guys that I see trying it are terribly inconsistent on their low strike, and tend to not give the high strike too often.
I use a modified GD stance. I am MUCH closer to the catcher, and do not work that high (which is dangerous! you are more apt to get hit by foul tips working that high....yes, I have tried the GD, and didn't like being that much of a target). I get my chin to the top of the catchers helmet (roughly).
Working three feet behind the catcher just doesn't work. Again, everybody I see calling from that far back usually has a major inconsistency in their strike zone, and it REALLY calls attention to itself! I hear coaches complain all the time about the local guys that use the GD, about how they are "too far back to call the low pitch right" is what I hear most often.
Oh well, those that use the GD are convinced that they are doing everything good. Whatever gets them through a game I guess.