I definitely agree with not going 9 pool, because it sets you behind by a lot and limits your options. Zerg build orders are tricky and depend on the situation. I usually do overpool to have lings earlier against rushers, or to help my allies if needed.
I haven't played in years, but I used to do a 6 pool ling rush occasionally. Just to make the people I played with paranoid. In future games they will likely spend recourses on early defence.
