Another item you may consider to dampen vibration is a shaft with a sensicore or similar insert.  It is basically a little plastic stick with foam swirling around it that goes in the butt end of the shaft.  Some of the True Temper shafts can be ordered with a sensicore already inside or you can purchase the inserts separately and put them in next time you change grips.  Just a thought that you could use with any of the iron heads you choose to cut down on vibration and this would work in addition to any insert on the back of the iron.