[RickinMA]

no offense to those that use them, but S400's are just "out of spec" or rejected S300's - Given how crazy so many golfers are about their equipment (myself included) I'm surprised they're as popular as they are.
I can completely understand companies using them in their wedges, they're cheap, they have a name buyers recognize, and with wedges, they're not as concerned with matching to the rest of the set. That said, I'm not sure they'd make a lot of sense in a set of irons. Just because they're heavier than S300's, you don't know where exactly in the shaft that extra weight is distributed, and you don't know if the shafts are any stiffer than regular on-spec S300s. (of course, they can be matched by a competent clubmaker, but at that point, you might as well just use a bunch of regular old Dynamic shafts and skip the "gold" part)

Anyway, the FST Pro Whites might lower ball flight a little bit and based on the price, I think they're a much easier $olution than some of the other shafts mentioned.
If price was no object, I'd say to maybe try some X100's or look for some of the KB Tour shafts or check with some of the sponsors for that tour version of the Dynamic Golds.