I have a set of Dynamic Gold S300 irons with sensicore inserts, used on 4i – LW. They look like new and I want to install other heads but soften the flex to Regular or Senior. They are standard length now. What would be the range of heads that I could use. i.e. Would a 7i head on the 4i shaft at 7i length be about what flex? If not possible I have 10 shafts for sale.