My HDCP floats around 7-8. I have a SIM in my garage with a GC2 and have done the same comparison as you. Forged or cast irons didn't seem to make that much of difference but when you add the spring face type irons, (T300, Callaway Epic Forged) into the mix the standard deviation was double that of a standard i210/Wilson V6 type iron. The spring face irons are longer but that is really not the goal is it?