Forgive my cynicism, but I recon this stuff about frequency response is just a clever marketing pitch invented by Fiberspar and has just been absorbed into windsurfing folk law as fact.
One can certainly feel the difference a light mast makes to swing weight, especially when the rig is being bounced over chop, but I don't know that this 'frequency response' thing is anything more than feeling that lack of swing weight.
My experience is that lighter (SDM) masts usually feel better until they break but the biggest benefit is a mast that suits the sail perfectly and that is not always the lightest one.
I have some 55% masts that rig my speed sails far better than 70% and 100% masts just because they have a slightly different curve, and the weight difference becomes insignificant compared with the benefits of the better shape. SDM 100% masts are just too fragile in my experience (comes back to the thin walls to stop them being too stiff) and I wouldn't buy anything more than 70-75% for normal use.
Didn't some of the big mast manufacturers have big failure rates with 100% racing masts a year or two back?
For RDM's or skinnies it is a different matter. They must have much thicker walls to gain the correct stiffness so 100% carbon works extremely well. The only downside with that is cost but since they generally last very long and well it is worth paying for.
The older I get, the better I was.