There were a few Ford Tech Service Bulletins about cackle-fix of #8 injector. Ford TSB 03-21-39 combined a couple of the previous TSB's and talks about trouble-shooting the #8 if you are suspicious. It says to check for proper fuel pressure, then check #8 cylinder compression, all before considering replacing the #8 with a special injector.
But like previously mentioned it sounds like it's more of a preference if you want to get ride of the cackle noise, and not a performance issue.
Someone correct me if I'm saying bad stuff here.