Tk Rocky hunter

So I am looking into some new arrows. I currently shoot Easton Fmj 340's out of my element rkt at 72#'s 29" draw with 28 inch arrows and a 100 grain point. My local pro shop guy told me I should go down to 400's because the rkt's should be a medium cam. I like the full metal jackets and i wouldn't mind going down to a lighter arrow to get a little more speed but i worry 400 is underspined. Opinions?